Blood: plasma and formed element

 Blood 

Blood performs several vital functions of the blood; hence it has been frequently referred to as the seat of the soul. It distributes nutrients, oxygen, detoxicating compounds, and maintains a uniforms body temperature. It is a carrier of hormones which control and integrate the activities of the various organs. It conveys antibodies and cells that protect the body from invading pathogens and also transport drugs administered to the body so that they may produce their therapeutic effects on specific sites of ailment. 

The blood also collects the waste material generated by the body's metabolic activities. The blood can carry out its functions efficiently only if it is kept circulating in the body. This is affected by the heart which acts as a pump, and an intricate system of distributing pipes the blood vessels, viz, arteries, veins and capillaries. The heart and the blood vessels together form the cardio-vascular system.

Blood as a fluid Tissue: -

In human beings there is about 90 ml of blood per kilogram of body weight. However, this volume depends on the age and health of the Individual. Blood has a specific gravity of 1.05 to 1.06, and a pH of 7.4. It is made up of a fluid matrix called Plasma, and several types of cells termed formed elements. These two components separate when blood is centrifuged. The plasma forms 54% of the blood volume and the cells 45%. The latter is reffered to as the hematocrit or packed cell volume(PCV). The plasma contains many inorganic and organic substances. The formed elements consist of red blood cells(RBC) or erythrocytes, white blood cells(WBC) or leucocytes, and platelets or thrombocytes.

PLASMA

Blood plasma is the straw colored fluid obtained when all formed element are removed from blood. The ratio of plasma to formed elements is held relatively constant by the homeostatic controls of the body. The plasma contains inorganic salts with a dominance of chloride (Cl), sodium (Na+), and calcium (Ca++) ions, and lesser quantities of potassium(K+) and magnesium (Mg++) ions. Smaller concentrations of bicarbonate, sulphate, and phosphate, and traces of iron, copper, and iodine are also present.

The Plasma also contain glucose which is used as a principal energy source in cellular metabolism. A variety of other substances, such as amino acid, vitamins, lipids (neutral fats and cholesterol), hormones, urea, uric acid, and other metabolite waste produces are also present in the plasma. In addition, it contains dissolved oxygen, carbon dioxide, and nitrogen. Plasma also reflects certain abnormal conditions occurring in cells and tissue of the body. For example, within few hours following a heart attack, there is a noticeable increase in the level of the enzymes transaminase and lactic dehydrogenase in the plasma arising from the affected heart muscles. This has proved to be of significant value to a clinician is the diagnosis of heart attacks.

The plasma of a man contains about 70g proteins/L. Some of these proteins possess enzymic activity (e.g., phosphatases), While other function shows no activity at all. The function of the plasma proteins can be summarized as follow: -

1. Lipoproteins carry lipids and also transport lipid soluble vitamins and steroids hormones.
2. They are amphoteric compound because they act both as acids and bases. At the pH of human blood (pH- 7.4) proteins behave as acids and combines with cations such as Na+ and form a buffer, they are however, weak buffers.
3. Being macromolecules plasma proteins create a colloidal osmotic pressure in the blood which is higher than the colloidal osmotic pressure in the blood which is higher than the colloidal osmotic pressure in the interstitial fluid. This favors the passage of interstitial fluid into the plasma Finally (4) plasma, proteins, prothrombin and fibrinogen participate in blood clotting. 

FORMED ELEMENT 

The formed elements consist of the erythrocytes, leucocytes, and the thrombocytes.

ERYTHROCYTES: -

The red blood cells or erythrocytes are small (diameter: -7.5 in man and 9.0 in elephant) biconcave dices. Mammalian erythrocyte, except for the camel does mot possess a nucleus. In contrast, other vertebrates possess a nucleus. The erythrocytes are immobile and move with the flow of blood stream. The average concentration of erythrocytes is approximately 5000000/mm3 of blood in the adult human female. The erythrocytes are reddish in colour due to the presence of a respiratory pigment hemoglobin. Each erythrocyte contains an estimated 200 to 300 million molecules of hemoglobin. The latter serves to transport oxygen and, do some extent carbon dioxide, to and form the lungs. Hemoglobin is easily removed when the cell is broken (or lysed) by exposure to a hypotonic medium, or water. the resulting structure of the erythrocyte is called a "ghost" which consists of a network of protein and lipids.

The average life span of an erythrocyte in man is about 120days the old erythrocytes are continuously breaking down and new once are formed. The erythrocytes are destroyed by the phagocytic macrophages found in the reticulo-endothelial system (in bone marrow, spleen, liver, etc.). The porphyrin section of the hemoglobin is catabolized and formed bile pigment (bilirubin and biliverdin). However, most of the iron is retained in the bone marrow to be again incorporated into new erythrocytes.

LEUCOCYTES: -

The leucocytes are nucleated cells and are somewhat larger than the erythrocytes the white blood cells are also less abundant than the red blood cells. There are 5000 to 9000 leucocytes/mm3 of blood. An increase in the number of leucocytes above 10000/mm3 of blood is known as leukocytosis is caused by violent exercise, infection, hemorrhage, and a high protein diet. Leucopenia results from malnutrition, deficiency of vitamin B12, folic acid, and pyridoxine. 

The leucocytes are classified into granulocytes and agranulocytes depending on the presence or absence of granules in the cytoplasm.

Granulocytes are divided into three basic types, viz., neutrophils, eosinophils, and basophils. This classification of the granulocytes is based on the nuclear structure and affinity of the cytoplasmic granules to dyes (acid or base). In the neutrophils the cytoplasm is filled with fine uniformly distributed granules which do not show any affinity to either acid or basic dyes, and hence the name neutrophil. The nucleus is polymorphic divided unequally in 3-5 lobes and separated by deep indentations or by narrow strands of chromatin, therefore neutrophils are also referred to as polymorphocytes. These form 65-75% of the total leucocytes. The size of each neutrophil range from 10-12u. The eosinophils are loaded with granules which are relatively bigger in size than in the neutrophils. The granules show affinity to the acid dyes such as eosin the latter imparts them an intense red colour, and hence the name eosinophils. These are also referred to as acidophils. The nucleus is bilobed and the two lobes are connected by a thin stand of chromatin. The eosinophils form 2-4% of the total number of leucocytes. In the basophil, the cytoplasm takes an intense blue colored with basic dyes. The nucleus in the basophil is irregularly polymorphic. The basophils have the least representation in the total leucocyte count the normal percentage is only 0.15.

Agranulocytes are of two types, viz, lymphocytes and monocytes. The structure of the nucleus of agranulocytes is not polymorphic and is therefore, different form that of the granulocytes. Lymphocytes fall into two categories- small and large lymphocytes. The nucleus of the small lymphocyte is larger and it almost occupied the entire cell leaving only a peripheral cytoplasm, whereas the largest lymphocytes have relatively more cytoplasm. The lymphocytes form the second largest group of leucocytes; the small lymphocytes constitute about 25% and largest lymphocytes about 3% of the total leucocytes. The size of the small lymphocyte is about 7u, Whereas it is 10-12u in the large lymphocytes.

In monocytes the cytoplasm is more abundant in relation to the nucleus; the nucleus is ovoid, kidney shaped or with  many indentations. Moreover, characteristically, the nucleus is always placed eccentrically in the cells. The monocytes form 5-7% of total leucocytes. There size range from 10-15u. 

The average life span of leucocytes is two days. All leucocytes defend the body against invasion by microorganism which are engulfed and digested by the leucocytes by a process known as phagocytosis. Additionally, the lymphocytes form antibodies against proteinaceous matter gaining entry into the body. The relative ratio of the leucocytes changes during many diseases. This phenomenon is of great use to pathologists in diagnosis of diseases. For example, the concentration of eosinophils increases significantly during infection by worms, and in allergic conditions such as asthma and hay fever. 

Leukemia is very serious disorder of the body. This is a form of blood cancer and is characterized by an uncontrolled increase in the number of leucocytes (up to 1000000/mm3 of blood), with the appearance of immature forms in the blood stream. Leukemia is accompanied by anemia and is eventually fatal because the bone marrow cells that normally produce erythrocytes are displaced by leukemia cells. 

Thrombocytes or platelets: - In addition to the erythrocytes and the leucocytes, thrombocytes or platelets are another group of a formed the leucocytes, thrombocytes or platelets are another group of formed elements observed in the blood. These are small fragments (2-5u) of cells which lake nuclei, and function in blood clotting. They are oval in shape and have the capability of amoeboid movements. There are 250000 platelets/mm3  of blood. The life span of the thrombocytes is also very short perhaps only a few days in duration.

Spermatogenesis | Sperm | Oogenesis | Menstrual cycle |

  Gametogenesis  

It is the process of producing haploid gametes from diploid germ cells in the gonads, i.e. sperms and ova are produced in the testis and ovary, respectively. It is of the following two types (7) Spermatogenesis (17) Oogenesis 

💥Spermatogenesis: -

It is the production of sperms in males. 

(i), In tastes the immature male germ cells (spermatogonia) produce sperms by spermatogenesis that begins at puberty. 

(ii) Spermatogonia (sing. spermatogonium) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers.

(iii) Each spermatogonium is diploid and contains 46 chromosomes. Some of the spermatogonia called primary spermatocytes periodically undergo meiosis. 

(iv) The primary spermatocytes undergo first meiotic division leading to two equal, haploid cells called secondary spermatocytes, which contains only 23 chromosomes each.

(v)The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids which contain only 23 chromosomes each.

(vi) The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis. Thus, each sperm too contains only 23 chromosomes.

(vii) Sperm heads are embedded in the Sertoli cells and are finally released from the seminiferous tubules by the process called spermiation.

Role of Hormones in Spermatogenesis: -

The following hormones play an essential role in spermatogenesis.

(i) Spermatogenesis starts during puberty with the significant increase in hypothalamic hormone called Gonadotropin Releasing Hormone (GnRH). 

(ii) The increased level of GnRH acts on the anterior pituitary gland and stimulates the secretion of two gonadotropins, i.e., LH (Luteinizing Hormone) and FSH (Follicle stimulating Hormone) 

(iii) LH acts on the Leydig cells and stimulates the synthesis and secretion of androgens, which in turn stimulate the process of spermatogenes1s. 

(iv) FSH acts on Sertoli cells and stimulates the secretion of some factors, which help in the process of spermiogenesis.

💥Structure of a Sperm: -

(i) A sperm is composed of a head, neck, a middle piece and a tail. 

(ii) A plasma membrane encloses the whole body of sperm. 

(ii) Head contains an elongated haploid nucleus, the anterior portion of which is covered by a cap-like structure called acrosome. 

(iv) The acrosome is filled with enzymes that help in fertilization of the ovum. 

(v) Neck contains two centrioles, a proximal centriole, which is necessary for first cleavage division of zygote and a distal centriole, that gives rise to axial filament of tail. 

(vi) Middle piece possesses many mitochondria to produce energy for the movement of tail to facilitate sperm motility. 

(vii) Tail of the sperm consists of an axial filament. It helps in the movement of sperm inside the female reproductive tract towards the ovum for fertilization.

0ogenesis: -

It is the process of formation of a female gamete or ova in the ovary. 

(i) It starts during embryonic stage in a female. 

(ii) About a million oogonia are formed in the ovary of the female fetus which is 25 weeks old. No new oogonia are formed after birth.

(iii) The oogonial cells start meiotic division, enter into prophase I, get temporarily arrested at that stage and are called as primary oocytes.

(iv) Each primary oocyte then gets surrounded by a layer of granulosa cells called primary follicle.

(v) A large number of primary follicles degenerate during the phase from birth to puberty. As a result, about 60,000-80,000 primary follicles are left in each ovary at puberty.

(vi) The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles.

 

(vii) The thecal layer in secondary follicles becomes organized into an outer theca externa and an inner theca interna. This stage is called tertiary follicle. 

(viii) Tertiary follicle is characterized by a fluid-filled cavity called antrum. 

(ix) At this stage, the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. 

(x) The first meiotic division, which is unequal results in the formation of haploid secondary oocyte and tiny first polar body. 

(xi) Secondary oocyte retains bulk of the nutrient rich cytoplasm of the primary oocyte. 

(xii) The tertiary follicle develops into a mature follicle or Graafian follicle. 

(xiii) The secondary oocyte forms a new membrane called zona pellucida surrounding it.

(xiv) The Graafian follicle ruptures to release the secondary oocyte (ovum from the ovary by the process called ovulation.

Ovum: -

Human egg or ovum is non-cleidoic (i.e. without shell), alecithal (i.e. yolk is absent), microscopic with about 0.1 -0.13 mm or 100-130 um diameter. The ovum possesses three coverings, i.e. inner plasma membrane, middle glycoprotein, zona pellucida and outer cellular corona radiata with radially elongated scattered cells held in mucopolysaccharide (hyaluronic acid).

✒ Menstrual Cycle: -

It is a rhythmic change in the reproductive organs of the female primates (monkey, apes and humans). 

(i) The first menstruation begins at puberty and is called menarche. 

(ii) Average interval of menstruation in human female is about 28-29 days. 

(iii) The cyclic events starting from one menstruation till the next one constitutes one menstrual cycle. 

(iv) The four phases of menstrual cycle are: -

✅Menstrual Phase: -

(a) Cycle starts with this phase and the menstrual flow occurs for 3-5 days.

 (b) It occurs due to breakdown of endometrial with lining of the uterus and blood vessels which along unfertilized ovum comes out through the vagina. 

(c) Menstruation occurs only if fertilization does not take place.

(d) Lack of menstruation generally indicates pregnancy, but may also be due to stress, poor health, diseases, etc. 

✅Follicular or Proliferative Phase: - 

(a) Menstrual phase is followed by the follicular phase.

(b) The primary follicle in the ovary grows to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation.

(c) Pituitary and ovarian hormones induce the changes in ovary and uterus. 

(d) LH and FSH levels increase gradually during this phase and stimulates follicular development. 

(e) The growing follicles secrete oestrogens. 

(f) Both LH and FSH attain highest level during mid-cycle (about 14th day)

✅Ovulatory Phase: -

(a) Rapid secretion of LH leading 1o its maximum level during the mid-cycle is called LH surge. 

(b) The LH surge induces rupture of Graafian follicle, releasing the ovum and this process is called ovulation.

✅Luteal Phase/Secretory Phase: -

(a) Ovulatory phase is followed by the luteal phase. 

(b) The remaining parts of the ruptured Graafian follicle change into corpus luteum. 

(c) Corpus luteum secretes large amount of progesterone, which is required for the maintenance of endometrium. 

(d) The thickened endometrium is necessary for the implantation of fertilized ovum and maintenance of pregnancy. 

(e) During pregnancy, all the events of menstrual cycle stop, and menstruation does not occur. 

(f) In case of no fertilization, the corpus luteum degenerates and now known as corpus albicans, which does not secrete progesterone. This causes rupture of endometrium leading to menstruation - initiation of a new cycle. 

(v) In human females, menstrual cycle stops around the age of 50 years and this phase is called as menopause. 

(vi) Menstrual cycle is absent temporarily during pregnancy and lactation periods and permanently after menopause. 

(vii) Menstruation is also called 'Weeping of uterus for the lost ovum' or "Funeral of unfertilized eggs'.

Human Reproductive system, Male Reproductive System, Female Reproductive System, Mammary glands,

Human Reproductive system

✅ Male Reproductive System: -

It includes a pair of testes, accessory ducts, glands and the external genitalia. 

(i) Testes are located outside the abdominal cavity within a pouch called scrotum which maintains the low temperature of the testes (2-2.5°C lower than the normal body temperature) required for spermatogenesis.

(a) Each testis is oval shaped with a length of 4-5 cm, width of 2-3 cm and covered by a dense covering called tunica albuginea.

(b) Internally it is divided into about 250 Compartments known as testicular lobules. 

(c) Each lobule contains 1-3 highly coiled structural and functional units of testis called seminiferous tubules in which sperms are produced. 

(d) Seminiferous tubule is lined on its inside by two types of cells called male germ cells or spermatogonia and Sertoli cells 

(e) Male germ cells undergo meiotic divisions leading to the formation of spermatozoa. 

(f) Sertoli cells provide nutrition to the germ cells and hence called nurse cells. 

(g) Interstitial spaces are present in between the seminiferous tubules which contain small blood vessels and Interstitial cells or Leydig cells. 

(h) Leydig cells synthesis and secrete the testicular hormones called androgens mainly testosterone.

(ii) Male accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens. 

(a) The intratesticular duct system starts with tubuli recti, which are short, straight end segments of the seminiferous tubules. These tubules connect the seminiferous tubules to the highly anastomosing, cuboidal epithelium-lined channels called rete testis.

(b) From rete testis, 10-25 fine tubules arise called vasa efferentia that leave the testis and open into the epididymis. 

(c) Epididymis leads to vas deferens that ascends to the abdomen and loops over the urinary bladder. It receives a duct from the seminal vesicle to form ejaculatory duct that runs through the prostate and opens into urethra. 

(d) Urethra receives the ducts of prostate gland and the bulbourethral gland (Cowper's glands) a little ahead and runs through the penis to its external opening called urethral meatus.

(iii) The accessory glands of male reproductive system include 

(a) A pair of seminal vesicles, a prostate gland and a pair of bulbourethral glands (Cowper's glands). 

(b) The secretion of all these glands is called seminal plasma. 

(c) Seminal vesicles secrete alkaline seminal fluid that contains fructose, citrate, prostaglandins, etc. 

(d) Prostate gland secretes slightly acidic (pH-6.5) milky fluid containing calcium proteolytic enzymes, etc. This fluid nourishes and activates spermatozoa to Swim, i.e., it provides sperm motility. 

(e) Secretion of bulbourethral glands is alkaline, and it helps in the lubrication of the urogenital tract. It also neutralizes any acid of urine present in urethra. 

(f) Seminal plasma along with sperms is called semen. 

(iv) External genitalia are the penis. It is made up of special erectile tissue that helps in erection of the penis. The enlarged tip of the penis is called glans penis. It is covered by a loose fold of skin called foreskin or prepuce.

Female Reproductive System: -

It consists of a pair of ovaries, secondary sex organs, external genitalia and mammary glands. 

(i) Ovaries are primary female sex organs. which produce female gametes called ova and secrete the female sex hormones. 

(a) These are located one on each side of the lower abdomen. 

(b) These are almond-shaped, 2-4 cm in length and 1.5 cm in width. 

(c) Each ovary is connected to the pelvic wall and uterus by ligaments. 

(d) Each ovary is covered by a thin epithelium which encloses the ovarian stroma.

(e) Ovarian stroma is divided into two regions, i.e., peripheral cortex and inner medulla. 

(ii) Other structures associated with female reproductive system are accessory ducts or oviducts or Fallopian tubes, uterus and vagina. 

(iii) Each Fallopian tube is about 10-12 cm long and extends from the periphery of each Ovary to the uterus. 

(a) The part of oviduct closer to the ovary is funnel-shaped and is known as infundibulum. 

(b) The edges of infundibulum possess finger-like projections called fimbriae, which help in the collection of ovum after ovulation. 

(c) Infundibulum leads to a wider part of the oviduct called ampulla.

 (d) Isthmus is the last part of the oviduct, which has a narrow lumen, and it joins the uterus 

 Figure 3.2 Female reproductive system (a) Lateral view (b) S

(iv) Uterus or womb is a pear-shaped muscular organ. It is about 75 cm long and 5 cm wide. It is attached to the pelvic wall and supported by ligaments. 

(a) Wall of the uterus has three layers of tissue. 

(b) Perimetrium is the outermost thin membranous layer, myometrium is the middle thick layer of smooth muscles and endometrium is the innermost glandular layer which lines the uterine cavity. 

(c) Uterus opens into the vagina through a narrow cervix, its cavity is called cervical canal, which along with vagina forms birth canal. 

(d) Endometrium layer undergoes cyclic changes during menstrual cycle. 

(e) Smooth muscles in myometrium contract during parturition to deliver the baby. 

(v) Vagina is a muscular tube-like structure that opens to the outside. It receives spermatozoa during insemination and serves as birth canal. 

(vi) Female external genitalia

✒Include mons pubis, labia majora, labia minora, clitoris and hymen. 

(a) Mons pubis is a cushion of fatty tissue covered by skin and pubic hair. 

(b) Labia majora are fleshy folds of tissue which extend down from the mons pubis and surround the vaginal opening. 

(c) Labia minora are paired folds of tissue under the labia majora.

(d) Hymen is a membrane that covers the opening of vagina partially. It gets ruptured during vigorous physical activities or during the first coitus. 

(e) Clitoris is a tiny finger-like structure, which lies at the upper junction of the two labia minora above the urethral opening. It is homologous to male penis. 

(vii) Mammary glands (breasts) are paired structures that contain glandular tissue and variable amount of fat. 

(a) Glandular tissue of each mammary gland is divided into 15-20 mammary lobes containing the cluster of cells called alveoli. 

(b) The cells of alveoli secrete milk, which is stored in the cavities (lumen) of alveoli. 

(c) Alveoli open into mammary tubules. The tubules of each lobe join to form a mammary duct.

(d) Several mammary ducts join to form a wider mammary ampulla, which is connected to lactiferous duct through which milk is sucked out.