human reproduction//male reproductive system, male germ cell, scrotal cell, testes, penis.

 Scrotal sac

In human males, the testes are situated outside the abdominal or pelvic cavity in a sac of skin called the scrotal sac. It acts as thermoregulation to keep the testicular temperature 2-3c lower than the optimum temperature necessary for sperm production (spermatogenesis).  It is biologically homologous to the major in females. 

Testes

These are the primary male gonads in man. Each testis is oval in shape, with a length of about 4-5 cm and a width of 2-3 cm. They develop in the scrotum by a spermatic cord in the later stages of life.

Cremaster muscles and dortas muscles of the scrotal sac help in the positioning of the testes. Whenever the temperature is low, these contract to move the testes close to the abdomen or pelvic cavity and vice-versa.

Note * Cremaster muscle and connective tissues surround all structures passing through the inguinal canal including the spermatic cord. 

* If testes fail to descend, this condition is called cryptorchidism, which leads to sterility. inflammation of the testis is called orchitis.

* Gubernaculum is a fibrous cord that extends from the caudal end of the testis to the scrotal wall.

Tunica of testis

The testis is surrounded by three protective coverings known as tunicates. These are as follows:

(1) Tunica vaginalis It is the outer covering of the testes.

(2) Tunica albuginea It is the white fibrous capsule that sends partitions through its interior surface to divide the testis onto lobules.

(3) Tunica vasculosa contains a network of capillaries that are supported by delicate connective tissue.

Seminiferous tubules

Each testies has about 250 compartments called testicular lobules and each lobule contains one to three highly coiled seminiferous tubules, where the sperms are produced. Seminiferous tubules from loops at both ends, which continue as a short segment of straight tubules, the tubuli recti. These tubules connect the seminiferous tubules to a highly anastomosing labyrinth of cuboidal epithelium-lined channels, the rete testis, which gives rise to 10-12 fine tubules called ductules efferentes.

Tubuli recti, rete testis, and ductile efferentes from the intertentacular genital duct systems. the tubules of ductuli efferentes combine to form the ductus epididymis.

The stratified epithelium of the seminiferous tubule is made up of three types of cells.

(1) Sertoli cells (supporting cells) These are also called sustentacular cells or nurse cells. They are elongated and pyramidal, which partially envelope the spermatogenic cells. This cell secret a glycoprotein hormone called inhibin, which is involved in the negative feedback control of sperm production by checking FSH activity.

(2) Spermatogenic cells Line the space between the basal lamina and the lumen of the tubule. These cells divide several times and differentiate to produce spermatozoa.

(3) Leydig cells (interstitial cells) They are a group of polyhedral cells and are present between the seminiferous tubules.

These cells secrete the testosterone hormone that controls spermatogenesis. These are endocrine in nature and are a characteristics feature of the testes of mammals.

Vasa efferentia(Sing. vas efferens)

A set of about 10-20 vasa efferentia collects from inside the testis and transfers them to the epididymis through rete testis. It has large columnar ciliated cells and small non-ciliated cells with endocytic activity, which help in conducting sperms.

Epididymis 

The epididymis is a coiled tube, which consists of three parts. The anterior end called caput epididymis, middle part corpse epididymis, and the posterior end is cauda epididymis. It is lined with pseudostratified columnar epithelium. It stores by sperm temporarily and produce essential chemicals required for the nourishment and maturation of sperms.

Vasa deferentia

It is a straight tube, which carries sperms to the urethra. Most of the sperms are stored in vas deferens. vas deferens is also called ductus deferens or sperm duct. It arises from cauda epididymis, ascends to the abdomen, passes over the urinary bladder, and receives the duct from the seminal vesicle behind the urinary bladder forming an ejaculatory duct. it passes through the prostate to open the ejaculatory duct. it passes through the prostate to open into the urethra shortly after its origin from the urinary bladder.

Urethra

It carries urine from the bladder as well as, sperms from the vas deferentia, through the penis. Thus, it is known as urinogenital as it provides a common pathway for the flow of both urine and semen.

It comprises three regions

(1) A short proximal prostatic urethra surrounded by the prostate gland. 

(2) A very short middle membranous urethra without covering.

(3) A long distal penile urethra that passes through penis.

penis

It is male external genitalia. It is vascular, spongy contains erectile tissue and a pensile organ suspended from the public region in from public region in front of the scrotum. During sexual arousal, erectile tissue fills with blood, causing the penis to become hard and erect to facilitate copulation and transmit sperms into the vagina of the female. Therefore, it is also called a copulatory organ. it has a glance penis at the tip, which is covered with a loose fold of skin called the prepuce or foreskin. The margin of glance penis is known as Corona.

The interior of the penis consists of three cylindrical cords made of spongy and erectile tissue. Two of them are parallel and called corpora cavernosa, which become superior-posterior when the penis is erect. The third, spongiosum corpora urethrae remain inferior-anterior in an erect penis. It is called so because the urethra runs from this cord. The pineal mass is covered by a dense connective tissue,m called tunica albuginea. Tyson's gland or preputial gland present in the penis neck secret a white sebaceous substance called smegma.

Regeneration, regeneration in animals, regeneration in planaria, regeneration in hydra.

 REGENERATION

It is the capacity of the body to produce the lost part of the proliferation of the cells. Regeneration leads to the healing of wounds, replacing worn outcall, and even the formation of the complete individual. 

Types of regeneration 

There are mainly two types of regeneration. These are as follows 

1. Reparative regeneration 

It is localized cell proliferation and cell migration leading to repair or headline. It is quite common in both invertebrate and vertebrate groups, e.g earthworms, amphibians, salamanders, and axolotl larvae. Reparative regeneration also involves compensatory hypertrophy, i.e. growth of a part that is removed or damaged. 

2. Restorative regeneration

It is the restoration or replacement of a lost body part. In this process, even a complete organism can be formed from a fragment of a body, e.g. in Hydra, Planaria, and sponges.

Restorative regeneration decreases with the increase in complexity of the organization of animals. It involves the differentiation of cells, mitotic divisions, cell movements, etc.

Mechanism of regenration

TH Morgan recognized two primary mechanisms of regeneration. These are as follows

(1) Morphallaxis  (Morpholloactic regeneration)

It involves the reconstitution of the body from small fragments by the reorientation and reorganization of the existing body cells. The regenerated animals are smaller than the original ones after the completion of the process, e.g. hydra.

(2) Epimorphosis (Epimorphic regeneration)

It takes place by the proliferation of new cells from the surface, tail in lizard, etc. In the case of crustacean, if the antenna is cut, etc. In the case of crustacean, if the antenna is cut, it may be replaced by an eye or vice-versa. This is called heteromorphisms. in the regeneration of mammalian liver or kidney, the cells divide, but do not form an undifferentiated mass of cells or tissues. These produce cells similar to themselves and maintain their differentiated function. This intermediate type of regeneration is called compensatory regeneration.

Examples of regeneration 

Regeneration occurs in the organism of almost every class some example of regeneration occurring to the groups are given below

Protozoans:

Ciliated like Stentor, Blenpharisma, and Spirostomum required only cell cortex for regeneration. About 1/100th part of the body of Acetabularia can regeneration the entire body.

Poriferans

They possess the remarkable power of regeneration. Any part of the body cut off or injured is readily repaired. Small pieces of sponges (containing amoebocyte) can grow into a compiled individual. 

Coelenterates

Hydra has excellent power of regeneration that was discovered by Trembley. he cut the body into sections and the lost part is regenerated with exact polarity. in hydro, it is the interested cell, which is totipotent and responsible for Completed regeneration. in hydra, regeneration will be faster if it is cut off from tentacles. hydra has a unique capacity of regenerating its hypostome (Ireland) again and again. this is called repetitive regeneration that has made it virtually immortal.

Planarians

(Platyhelminthes) They have a stock of undifferentiated cells called neoblasts, which are omnipotent. They may regeneration the cut portions, lost parts, and whole body. Planaria show super regeneration, i.e. the development of cells or organs in a number that is more than required.

Annelids Sealing of the wounds by neoblast cells.

Mollusca Regeneration is poor in gastropods. Eye stalk with the eye may be regenerated. Cephalopods may regeneration their arms.

Nematodes Regeneration is poor, only closure of the superficial wound is observed.

Arthropods Limited renewal of lost appendages as in certain crustaceans and spider takes place by regeneration.

Echinoderms  Starfish, brittle stars, and sea lilies can regenerate arms and parts of the disc.

Fishes   Regeneration restricted to fish fins.

Amphibian Limb regeneration. 

Reptiles Lizards are known to regenerate their tails which they lose by autotomy, i.e. self-amputation of a part of the body when threatened by a predator.

Birds Parts of the beak can be regenerated, otherwise, the regenerative ability is poor.

Mammals Extremely poor regenerative capacity, few marsupials can regenerate part of the limbs and liver.

                                          

                                                             

Pre-Mendelian experiment || Mendel's Laws of Inheritance// Heredity and variation

 Pre-Mendelian experiment 

As we know, reproduction in living organisms is done to facilitate the continuity of life. The progeny produced, often resemble their parents in most of the characteristics. This passage or transmission of characters from parents to their offsprings is called Heredity and the process by which characters from one generation to the next is called inheritance. However, all characteristics of offspring are not similar to their parents. Some of them show variations or changes also. These variations signify their own characteristics.

The study genetical of heredity and variation is called genetics. This term was proposed by William Basten's in 1905. The basic principles of genetics were discovered by Mendel in (1822-84). The medal is also known as the 'father of genetics'.

                                                              

Branches of genetics

Geneticists (the scientists who the process of genetics) often divide genetics into the following three main branches,

(1) Trancemission genetics is also called classics genetics. It involved the transmission of genetic material from one generation to another. it is further subdivided into Mendelian genetics, Morganton genetics (i.e. recombination in all kinds of organisms), non-Mendelian genetics, and mutation.

(2) Molecular and biochemical genetics involve the study of structural and functional aspects of genes at a molecular level.

(3) Population and biometric genetics involve the study of behaviour and effect of genes in various biological populations.

Heredity

It is defined as the transmission of structural, functional and behavioural characteristics from one generation to another. Thus, for a generation, it is the sum of genetic endowment obtained from their parents. Thus, for a generation, it is the sum of generation endowment obtained from their parents. The initiation of genetics work is attributed to Mendel. Genetics can be categorised into Pre-Mendelian, Mendelian and Post-Mendelian eras of working.

Pre-mendelian concepts of inheritance(theories of blending inheritance)

Before the idea of Mendel was accepted, there were many philosophers, thinkers and workers who gave various theory to explain heredity or inheritance. These theories are called Pre-Mendelian concept of heredity. Some of these are as follows, 

1.Moist vapour theory Pythagoras (580-500 bc) propose that various body part emit certain vapour, which gets aggregated to form a new individual. 

2. Flud theory Empedocles (504-433) through that every part of the body produces a fluid. This fluid then mixes up to form an offspring. Any defect in this fluid result in the formation of defective organs.

3. Preformation theory this was given by Swammerdam (1679) and by Malgiphi (1673). They believe that the Minature form of an individual is already present in the sperm or egg called 'homunculus'. Fertilisation is required and nassory to stimulate its growth. 

4. particulate theory Maupertius (1689-1759) Propose that various part of the body produce minute particles for reproduction. An individual is formed when the particles from the male and female unit.

5. Theory of pangenesis Darwin (1868) proposed that each body part produces a gemmule or Pantene. These pangenes carry parental strategies as well as variation. Their aggregation result to form gametes. On fusion, these rise to a new individual.

Pre-Mendelian experiment

Among the workers who performed the experiment before Mendel was a German botanist who works on the tobacco plant.

Other persons who worked on hybridisation before Mendal, include Bartner (1722-1850), Naudin (1815-1899) caught (1799) and goss (1824). but none of these workers was able to rationalise and explain the result which a sure degree of repetitions.

what is the growth? factory of growth|| imp information about information?????

 growth

                                                 

growth in living beings can be defined as the irreversible increase in overall size and weight of an organism due to the synthesis of new protoplasm.

forms of growth

In living organisms, growth can occur in two following forms.

Intussusception: It is an internal type of growth. In this form, the surface area of the cell increasing via deposition of any external material, that is synthesized by the existing body cell.

Apposition It is an external type of growth in which the surface area of the cell increase via deposition of any external material, this is not the constituent of the cell. Non-living, like mountains, sand mouth, and snow also grow by apposition, if the increase in body mass is the criterion. however, this growth is by the accumulation of material on the surface only.

Features of growth

At the cellular level, growth involves

1. Increase in size of the cell due to the synthesis of protoplasmic structure (hypertrophic) 

2. increase in the number of cells by cell division ( hyperplasia )

3. Increase in the amount of apoplastic structure like the fibres, material, etc.

Different cells may grow differently in humans for examples

1. Lens cells grow by multiplication.

2. Cardiac and skeleton muscle cells grow by the increase in volume.

3. Newron growth by extension and growth of the axons and dendrites.

4. Cartilage and bone cell growth by the secretion of extracellular Matrix.

Pattern of growth

On the basis of changes in body proportions, there are two types of growth patterns.

(1) Isometric growth It is a type of growth in which all the parts grow at the same rate and same time Thus, there is no change in the form and body proportion, e.g. fish, locust, and grasshopper.

(2) Allometric growth It is a type of growth, in which different organs grow at a different rate and at different time. Thus, the external form and body proportion change which the stage of growth, e.g. mammals.

Types of growth

The different types of growth in the bodies of a living organism are 

(1) Auxetic growth It is the growth due to the increase in the size of cells (not a number), e.g. nematodes, rotifers, and tunicates (early chordates).

(2) Multiplicative growth It is the growth of the body due to the increase in the no of cells, e.g. embryonic development of higher vertebrates.

(3) Accretionary growth   It is the growth in which undifferentiated reserve cells get differentiated to perform a specific function, e.g. formation of erythrocytes from erythropoietic tissue, replacement of worn-out cells of the skin, secretion of extracellular matrix by chondrocytes and bone osteocytes.

Growth curve

It is a graphic representation of growth against time. The sigmoid curve or S-shaped growth curve is the characteristic growth curve of all higher animals including humans. In the initial phase, The curve rise at a very slow rate.

In the middle part, the curve rises steeply indicating a very fast rate of growth (acceleration phase). Finally, in the last part, the rate of growth again slows down till the curve becomes horizontal (Plateau phase).

It signifies that no further growth is taking place and the individual is simply itself. Hence, animals show a differential growth rate.

An absolute growth rate curve shows how much the rate of growth changes with time, whereas a relative growth rate curve is taken into account the existing size.

Positive and negative growth 

Positive growth occurs when the synthesis (anabolism) of the material exceeds the crackdown (catabolism) of the material. in some cases, continuous positive growth is non-vertebrates, fish, and certain some reptiles. in such cases, growth may continue to rise slightly until the organism dies.

Negative growth occurs when catabolism exceeds anabolism. It is during the germination of seeds. Germination of seeds includes a period of negative growth, which becomes positive when seedlings start to photosynthesis and make their own food. In certain cnidarians, the growth curve flattens out, indicating zero growth.

Growth in human

the human body undergoes the following pre-birth phase of growth.

                                                    

1. cellular growth

The unicellular organism grows only through cell growth. In a multicellular organism, growth is the sum total of growth shown by their cells. The steps involved in cellular growth initiate with cell division following by cell enlargement and cell differentiation finally leading to maturation. cell growth occurs during the post-mitotic phase and interphase.

2. Embryonic growth

In humans, the early embryonic development stage constitutes transitional growth. During cleavage and blastula formation, the cells exhibit little growth.

During gastrulation (early embryonic state), rudiments of primary organs develop, but they are in their functional state. with further development, the rudimentary organs grow, differentiate, and become functional.

The overall growth of the fetus occurs mainly in the period after the basic morphological plane is established, i.e. 

Post-embryonic growth

East animals have a specific rate and rhythm of growth. There is no uniformity in the rate of growth. Animals grow at different rates at different periods of life. The human embryo is about 150-micro meters at the time of implantation, which grow about 50 cm over the 9 months of gestation. embryos can not grow considerably during the first 2 month after implantation as it is a time for the formation of basics human body structure. after four months, the embryo grows 10 cm/ month and during the first year, 2 cm/month and it stops after 22-33 yrs of age. 

Control of growth

Growth depends on growth factors and hormones. The various growth factors involved in the control of growth in the human body are discussed in afters.

ape man || Homo habilis, Homo erectus discovery and characteristics

 Australopithecus africanus

                  Discovery

                                                  Prof. Raymond Dark (1924), a South African anthropologist discovered the skull of a 5-6-year-old baby, about 5 million years old near the Tuang river in Africa. This baby fossil is termed Australopithecus africanus ( African ape-man or Tuang baby),

                                                The 3.8 million-year-old fossils of a new species Australopithecus Africanus was first discovered by Mary Leakey from the volcanic ash of Lateral and later on Donald Johanson and Timothy D white established a new species.

                                               Zojanthropus (the old vain toolmaker) was discovered by Mary Leakey and LBS Leakey (1959) from Tanzania (East Africa) which has been named Australopithecus boisei by Leakey. 

                                            A. Africanus (African ape-man or southern ape-man or Tuang baby), A. boisei (Olduvai tool man), A. Afarensis (Lucy), Aramids, A. aethiopicus, and A. robustus are six known species of Australopithecus.

                 Characteristics

                                        Its height was 1.5 m and both human and ape's characters.

                         

                                       It was a fully bipedal hominid.

                                      It lived from 4-1.5 million years ago in caves during the Pleistocene period.

                                     It has an erect posture and an omnivorous diet.

                                     Its cranial capacity volume (brain size) was 500-700 cc,i.e. equivalent to a modern gorilla.

                                     Brown ridges projected over the eyes and lack chin.

                                   A distinct lumbar curve was present in the vertebral column.

                                 Its thigh and hips were adapted for erect standing, walking, and running.

                                  Its arms were somewhat less mobile than ours and pelvis were broad.

                                 Its ankle bone was intermediate between human and ape.

                              

                                 It had protruding jaws and a modern man like teeth.

                        

                               Its face was prognathous with larger jaws and teeth than modern man.

                               Australopithecus africanus gave rise to Homo habilis approximately 2 million years ago, also a separate line gave rise to Australopithecus robustus and Australopithecus boisei.

Homo habilis

                       Discovery

                                                Louis SB Leaky and his wife Mary Leakey (1961) obtained the fossils of homo habilis Pleistocene rocks of Olduvai Gorge in East Africa.

                                              Richrd Leakey (1972) also obtain fossils of Homo habilis from the east side of Lake Turkana in Kenya.

                      Characteristics

                                           Homo habilis is called the first toolmaker because he had developed the most primitive stone tools.

                                         Homo habilis man was about 1.2-1.5 m tall.

                                        Its cranial capacity was 700-800 cc, which lived in Africa about 2 million years ago.

                                    Homo habilis was carnivorous and begun hunting for meat.

                                  Homo habilis lived in small communities or groups in caves.

                                 Perhaps they show the sexual division of labor and communication with visual signals and simple audible sounds.

                                                                 

Homo erectus

                       Discovery

                                             Fossils of Homo erectus were obtained from diverse sites from Olduvai Gorge in Africa java, Algeria, Germany, Hungary, and china. 

                                              Fossils were 800000 to 30000 years ago.

                                             Homo erectus is considered the direct ancestor of modern man. It evolved from evolution.

                    Characteristics

                                         They were the oldest known early human to have modern human-like body proportions.

                                        There were the first human species to have a fleshy nose. they had a flat skull with prominent ridges over the brow.

                                      They had short arms and long legs. The long legs depict that they are better suited for long-distance migration

                                  They were the first ones to walk upright and stood erect thus, named so. They are also known as Homo register.  

Pithecanthropus erectus

                  Discovery

                                   In 1891 Eugene Dubois obtained fossils (some teeth, skull cap, and femur bone) from Pleistocene deposits (500000-1500000 year ago) in Central java (an island of Indonesia).

                             It was named Pithecanthropus erectus (ap man that can walk erect) by Eugene Dubois and Homo erectus by Mayer (1950)

    Characteristics

                             Java man was more than 1.65-1.75 m tall weight about 70 kg.

                             Its legs were long and erect, but its body slightly bent during movement.

                            The face of the Java man was prognathous, Whereas the forehead was low and slanting.

                          Its Java was large and heavy, but quite similar to those of modern man, except large canine of the lower jaw.

                         Its nose was flattened and chin inconspicuous along with thick and protruding lips.

                       Java man was omnivorous and cannibal.

                     Java man was the first prehistoric man, who began the use of fire for cooking, defense, and hunting.

                     Its crinal cavity was 940mcc, which is about intergraded between Australopithecus (600-700 cc) and modern man (1400-1600 cc). 

Sinanthrops

         Discovery

                       The fossil (skulls, jaws, and postcranial bone fragments) of parking man were discovered by W C PAI (1924) from the limestone caves of Choukoutien near Peking (Peking is the former name of china"s capital Beijing).

WC PAI named java man Sinanthropus, whereas Davision Black (1927) named it Sinanthropus Pekinensis, and Mayer (1950) called it HOMO Erectus Pekinesis.

          These fossils of Peking man was about six lakh year old.                                                                                                                                          

    

   Characteristics

     Peking man was1.55-1.60 m tall, i.e. slightly shorter, lighter, and weaker than java, man.

The cranial cavity of Peaking man was 850-1200 cc than is more than java man.

The peaking ape-man was omnivorous and cannibal.

  clear evidence has been obtained from Hungary and China in support of the use of fire by peaking man. These were hunters and food gatherers. 

Like java man, Peaking man also lived in caves in small groups or tribes or communities.

The peaking man was first to bigger with the uses of clothes ( made from animal skins), rudimentary languages, and tools made with woodman's bones.

Morphology was similar to a java man with heavy bony eyebrow ridges, a low slanting forehead, chinless face.