Specimen 1. Human pituitary gland (hematoxylin-eosin staining) Under a low magnification microscope, understand the topography of the pituitary gland formed by the anterior, intermediate and posterior lobes. Under high magnification, examine the anterior, intermediate and posterior lobes. Note the fibrous structure of the capsule surrounding the pituitary gland, in the anterior lobe - chromophobe adenocytes, acidophilic and basophilic adenocytes. Between the strands of glandular cells in thin layers of connective fibrous tissue, sinusoidal capillaries are visible. In the intermediate part there are small epithelial cells and pseudofollicles filled with colloid. In the posterior lobe there are glial cells - pituicytes, between which there are blood vessels and expanded terminals of the neurosecretory cells of the hypothalamus (Herring's bodies).
Specimen 2. Cat pituitary gland (hematoxylin-eosin staining). The specimen shows three lobes: anterior, intermediate and posterior. The intermediate lobe is separated from the anterior lobe by the falciform pituitary fissure. The pituitary gland is connected to the hypothalamus through the pituitary stalk.
1. The main stages of the formation of hemacytopoiesis and immunocytopoiesis in phylogenesis.
2. Classification of hematopoietic organs.
3. General morphofunctional characteristics of the hematopoietic organs. The concept of a specific microenvironment in the hematopoietic organs.
4. Red bone marrow: development, structure and functions.
5. The thymus is the central organ of lymphocytopoiesis. Development, structure and functions. Age-related and accidental involution of the thymus.
In the process of evolution, the topography of the hematopoietic organs (OCT) changes, their structure becomes more complex and their functions differentiate.
1. In invertebrates: there is still no clear organ localization of hematopoietic tissue; primitive hemolymph cells (amebocytes) are diffusely scattered throughout the tissues of organs.
2. In lower vertebrates (cyclostomes): the first isolated foci of hematopoiesis appear in the wall of the digestive tube. The basis of these foci of hematopoiesis is reticular tissue; there are sinusoidal capillaries.
3. In cartilaginous and bony fish, along with foci of hematopoiesis, separate OCTs of the spleen and thymus appear in the wall of the digestive tube; There are CT foci in the gonads, interrenal bodies and even in the epicardium.
4. In highly organized fish, CT foci first appear in bone tissue.
5. In amphibians, there is an organ separation of myelopoiesis and lymphopoiesis.
6. In reptiles and birds, there is a clear organ separation of the myeloid and lymphoid tissue; main OCT - red bone marrow.
7. In mammals - the main OCT is red bone marrow, in other organs - lymphocytopoiesis.
OCT classification:
I. Central OCT
1. Red bone marrow
II. Peripheral OCT
1. The actual lymphoid organs (along the lymphatic vessels - lymph nodes).
2. Hemolymphoid organs (along the blood vessels- spleen, hemolymphatic nodes).
3. Lymphoepithelial organs (lymphoid accumulations under the epithelium of the mucous membranes of the digestive, respiratory, and genitourinary systems).
General morphofunctional characteristics of OCT
Despite the significant diversity, OCTs have much in common - in the sources of development, in structure and functions:
1. Source of development - all OCTs are formed from the mesenchyme; the exception is the thymus - it develops from the epithelium of the 3rd-4th gill pouches.
2. Commonality in structure - the basis of all OCT is connective tissue with special properties - reticular tissue. The exception is the thymus: the basis of this organ is the reticular epithelium (reticuloepithelial tissue).
3. Blood supply OCT - abundant blood supply; have hemocapillaries of a sinusoidal type (diameter 20 or more microns; between the endothelial cells there are large gaps, pores, the basement membrane is not continuous - in places it is absent; blood flows slowly).
The role of reticular tissue in OCT
You remember that the RT consists of cells (reticular cells, in small quantities fibroblast-like cells, macrophages, mast and plasma cells, osteogenic cells) and intercellular substance, represented by reticular fibers and the main amorphous substance. Reticular tissue in OCT performs the following functions:
1. Creates a specific microenvironment that determines the direction of differentiation of maturing blood cells.
2. Trophism of maturing blood cells.
3. Phagocytosis and disposal of dead blood cells due to phagocytosis of reticular cells and macrophages.
4. Support-mechanical function - is a supporting frame for maturing blood cells.
RED BONE MARROW - central OCT, where both myelopoiesis and lymphocytopoiesis occur. In the embryonic period, the BMC is formed from the mesenchyme in the 2nd month, and by the 4th month it becomes the center of hematopoiesis. KKM is a fabric of semi-liquid consistency, dark red in color due to the high content of red blood cells. A small amount of CMC for research can be obtained by puncture of the sternum or iliac crest.
The stroma of the CCM is made up of reticular tissue, abundantly penetrated by sinusoidal hemocapillaries. In the loops of reticular tissue, maturing blood cells are located in islands or colonies:
1. Erythroid cells in their colony islands are grouped around iron-loaded macrophages obtained from old red blood cells that died in the spleen. Macrophages in the RMC transfer iron to erythroid cells, which is necessary for their synthesis of hemoglobin.
2. Lymphocytes, granulocytes, monocytes, and megakaryocytes are located in separate colony islands around the sinusoidal hemocapillaries. Islands of different sprouts intersperse with each other and create a mosaic picture.
Mature blood cells penetrate through the walls into the sinusoidal gamocapillaries and are carried away by the bloodstream. The passage of cells through the walls of blood vessels is facilitated by the increased permeability of sinusoidal hemocapillaries (slits, absence of basement membrane in places), high hydrostatic pressure in the reticular tissue of the organ. High hydrostatic pressure is caused by 2 circumstances:
1. Blood cells multiply in a confined space limited by bone tissue, the volume of which cannot change and this leads to an increase in pressure.
2. The total diameter of the afferent vessels is greater than the diameter of the efferent vessels, which also leads to an increase in pressure.
Age-related characteristics of CMC: In children, CMC fills both the epiphyses and diaphysis tubular bones, spongy substance of flat bones. In adults, the BMC in the diaphysis is replaced by yellow bone marrow (adipose tissue), and in old age by gelatinous bone marrow.
Regeneration: physiological - due to cells of class 4-5; reparative - grades 1-3.
THYMUS is the central organ of lymphocytopoiesis and immunogenesis. The thymus is formed at the beginning of the 2nd month of embryonic development from the epithelium of the 3-4 gill pouches as an exocrine gland. Subsequently, the cord connecting the gland with the epithelium of the gill pouches undergoes reverse development. At the end of the 2nd month, the organ is populated with lymphocytes.
The structure of the thymus - on the outside, the organ is covered with a thymus capsule, from which septa made of loose thymus extend inward and divide the organ into lobules. The basis of the thymic parenchyma is the reticular epithelium: the epithelial cells are branched, connected to each other by processes and form a looped network, in the loops of which lymphocytes (thymocytes) are located. In the central part of the lobule, aging epithelial cells form layered thymic bodies or Hassall bodies - concentrically layered epithelial cells with vacuoles, keratin granules and fibrillar fibers in the cytoplasm. The number and size of Hassall's bodies increases with age. Function of the reticular epithelium:
1. Creates a specific microenvironment for maturing lymphocytes.
2. Synthesis of the hormone thymosin, necessary in the embryonic period for the normal formation and development of peripheral lymphoid organs, and in the postnatal period for regulating the function of peripheral lymphoid organs; synthesis of insulin-like factor, cell growth factor, calcitonin-like factor.
3. Trophic - nutrition of maturing lymphocytes.
4. Support-mechanical function - supporting frame for thymocytes.
Lymphocytes (thymocytes) are located in the loops of the reticular epithelium, especially many of them along the periphery of the lobule, therefore this part of the lobule is darker and is called the cortical part. The center of the lobule contains fewer lymphocytes, so this part is lighter and is called the medullary part of the lobule. In the thymus cortex, T-lymphocytes are “trained,” i.e. they acquire the ability to recognize “theirs” or “theirs.” What is the essence of this training? In the thymus, strictly specific lymphocytes (having strictly complementary receptors) are formed for all possible conceivable A-genes, even against their own cells and tissues, but in the process of “training” all lymphocytes with receptors for their tissues are destroyed, leaving only those lymphocytes that are directed against foreign antigens. That is why in the cortex, along with increased reproduction, we also see mass death of lymphocytes. Thus, in the thymus, subpopulations of T-lymphocytes are formed from the precursors of T-lymphocytes, which subsequently enter the peripheral lymphoid organs, mature and function.
After birth, the mass of the organ increases rapidly during the first 3 years, slow growth continues until the age of puberty; after 20 years, the thymic parenchyma begins to be replaced by adipose tissue, but a minimal amount of lymphoid tissue remains until old age.
Accidental involution of the thymus (AIT): The cause of accidental involution of the thymus can be excessively strong stimuli (trauma, infections, intoxication, severe stress, etc.). Morphologically, AIT is accompanied by mass migration of lymphocytes from the thymus into the bloodstream, mass death of lymphocytes in the thymus and phagocytosis of dead cells by macrophages (sometimes phagocytosis of normal, not dead lymphocytes), proliferation of the epithelial base of the thymus and increased synthesis of thymosin, erasing the boundary between the cortical and medullary parts of the lobules. Biological significance of AIT:
1. Dying lymphocytes are donors of DNA, which is transported by macrophages to the lesion and used there by the proliferating cells of the organ.
2. Mass death of lymphocytes in the thymus is a manifestation of the selection and elimination of T-lymphocytes that have receptors against their own tissues in the lesion and is aimed at preventing possible auto-aggression.
3. The growth of the epithelial tissue base of the thymus, increased synthesis of thymosin and other hormone-like substances are aimed at increasing the functional activity of peripheral lymphoid organs, enhancing metabolic and regenerative processes in the affected organ.
32. Pituitary gland
The pituitary gland has several lobes: adenohypophysis, neurohypophysis.
The adenohypophysis is divided into anterior, middle (or intermediate) and tuberal parts. The anterior part has a trabecular structure. The trabeculae, strongly branching, are woven into a narrow-loop network. The spaces between them are filled with loose connective tissue, through which numerous sinusoidal capillaries pass.
Chromophilic cells are divided into basophilic and acidophilic. Basophilic cells, or basophils, produce glycoprotein hormones, and their secretory granules are stained with basic dyes on histological preparations.
Among them, there are two main types: gonadotropic and thyrotropic.
Some of the gonadotropic cells produce follicle-stimulating hormone (follitropin), while others are responsible for the production of luteinizing hormone (lutropin).
Thyrotropic hormone (thyrotropin) – has an irregular or angular shape. When there is insufficiency of thyroid hormone in the body, the production of thyrotropin increases, and thyrotropocytes are partially transformed into thyroidectomy cells, which are characterized by larger sizes and a significant expansion of the endoplasmic reticulum cisterns, as a result of which the cytoplasm takes on the appearance of coarse foam. In these vacuoles aldehyde-fuchsinophilic granules are found, larger than the secretory granules of the original thyrotropocytes.
Acidophilic cells, or acidophils, are characterized by large dense granules that are stained in preparations with acidic dyes. Acidophilic cells are also divided into two types: somatotropic, or somatotropocytes, producing growth hormone (somatotropin), and mammotropic, or mammotropocytes, producing lactotropic hormone (prolactin).
Corticotropic cells in the anterior pituitary gland produce adrenocorticotropic hormone (ACTH, or corticotropin), which activates the adrenal cortex.
The tuberal part is a section of the adenohypophyseal parenchyma adjacent to the pituitary stalk and in contact with the lower surface of the medial eminence of the hypothalamus.
The posterior lobe of the pituitary gland (neurohypophysis) is formed by neuroglia. The glial cells of this lobe are represented predominantly by small branched or spindle-shaped cells - pituicytes. The posterior lobe includes the axons of neurosecretory cells of the supraoptic and paraventricular nuclei of the anterior hypothalamus.
Innervation. The pituitary gland, as well as the hypothalamus and pineal gland, receive nerve fibers from the cervical ganglia (mainly from the upper) of the sympathetic trunk.
Blood supply. The superior pituitary arteries enter the medial eminence, where they break up into the primary capillary network.
endocrine gland hypothalamus pituitary gland
The pituitary gland is a component of the body's unified hypothalamophyseal system. Produces hormones that regulate the function of many glands internal secretion and communicates with the central nervous system. It is located in the pituitary fossa of the sella turcica of the sphenoid bone of the skull; It has a bean-shaped shape and very little mass. So, in cattle it is about 4 g, and in pigs it is less - 0.4 g.
The pituitary gland develops from two embryonic rudiments growing towards each other. The first rudiment - the pituitary pouch - is formed from the roof of the primary oral cavity and directed towards the brain. This is an epithelial rudiment from which the adenohypophysis subsequently develops.
The second rudiment is a protrusion of the bottom of the cerebral ventricle, therefore it is a brain pocket and the neurohypophysis is formed from it (Fig. 4 appendix)
Embryogenesis determined the structure of the organ - the pituitary gland consists of two lobes: the adenohypophysis and the neurohypophysis (Fig. 5, 6 appendix).
The adenohypophysis consists of the anterior, intermediate and tuberal parts. The anterior part is built of epithelial cells - adenocytes, forming cords (trabeculae) and delimited by sinusoidal capillaries of the secondary vascular network. The primary vascular network is located in the medial eminence. The connective tissue stroma of the adenohypophysis is poorly developed.
Adenocytes perceive dyes differently: cells that stain well are called chromophilic, and cells that stain poorly are called chromophobic (b). Chromophilic adenocytes can perceive either acidic or basic dyes, therefore the former are called acidophilic (c), the latter - basophilic (d).
Acidophilic cells make up 30-35% of all cells of the anterior pituitary gland. They have a round or oval shape, larger than chromophobe and smaller than basophilic adenocytes. The cytoplasm of acidophilus contains granules that stain with eosin; the nucleus is located in the center of the cell. It is adjacent to the Golgi complex, a small number of large mitochondria, and a well-developed granular endoplasmic reticulum, which indicates intensive protein synthesis.
Due to the different hormone-producing function and structure, cytoplasmic granularity, three types of acidophilic adenocytes are distinguished: somatotropocytes, lactotropocytes, corticotropocytes. Somatotropocytes produce somatotropic hormone, which stimulates the growth of tissues and the entire organism as a whole. Lactotropocytes produce prolactin (lactotropic hormone), which regulates the lactation process and functional state corpus luteum ovary. Corticotropocytes produce corticotropin, which increases the hormone-forming function of the adrenal cortex.
Secretory granules of somatotropocytes are spherical in shape, with a diameter of 200 to 400 nm (Fig. 7 appendix). Lactotropocytes have larger oval-shaped secretory granules with a length of 500-600 nm and a width of 100-120 nm. The secretory granules of corticotropocytes are covered on the outside with a bubble-shaped membrane and a dense core.
Basophilic adenocytes make up 4-10% of all cells of the anterior pituitary gland. These are the most large cells adenohypophysis. Their secretory granules are glycoprotein in nature and are therefore stained with basic dyes. There are two types of these cells: gonadotropic and thyrotropic. Gonadotropic cells produce follicle-stimulating hormone, which regulates the development of female and male germ cells, the secretion of the female genital organs, and luteinizing hormone, which stimulates the growth and development of the corpus luteum in the ovaries and interstitial cells in the testes (Fig. 8 Appendix). IN central zone gonadotropic basophil is located in the macula. This is an expanded cavity of the Golgi complex, pushing the nucleus, numerous small mitochondria, and membranes of the endoplasmic reticulum to the periphery of the cell. Basophilic gonadotropocytes contain granules equal to about 200-300 nm in diameter.
With a lack of sex hormones in the body, the diameter of the grain increases. After castration of animals, basophilic gonadotropocytes turn into castration cells: a large vacuole occupies the entire central part of the cell. The latter takes on a ring shape.
Thyroid-stimulating basophils (Fig. 9 appendix) are angular cells with fine (80-150 nm) granularity filling the entire cytoplasm. If the body lacks thyroid hormones, thyroidectomy cells develop. They are increased in size, with expanded cisterns of the endoplasmic reticulum, so the cytoplasm has a cellular appearance, larger secretion granules.
Chromophobe cells make up 60-70% of all cells in the anterior pituitary gland. This is a combined group, since it includes cells of different importance: cambial cells, different stages differentiation; have not yet accumulated specific granularity; cells that secrete secretions. Acidophilic and basophilic adenocytes subsequently develop from cambial cells.
The intermediate part of the adenohypophysis is represented by several rows of weakly basophilic cells. The secretion produced by adenocytes accumulates in the spaces between cells, which contributes to the formation of follicle-like structures. The cells of the intermediate part of the adenohypophysis are polygonal in shape and contain small glycoprotein granules measuring 200-300 nm. In the intermediate zone, melanotropin, which regulates pigment metabolism, and lipotropin, a stimulator of fat metabolism, are synthesized.
The tuberal part of the adenohypophysis is similar in structure to the intermediate part. It is adjacent to the pituitary stalk and medial eminence. The cells of this zone are characterized by weak basophilia and trabecular arrangement. The function of the tuberal part has not been fully elucidated.
It was said above that the hormone-producing function of the adenohypophysis is regulated by the hypothalamus, with which it forms a single hypothalamoadenopituitary system. Morphofunctionally, this connection is manifested in the following: the superior pituitary artery in the medial eminence forms the primary capillary network. Axons of small neurosecretory cells of the nuclei of the mediobasal hypothalamus form axovascular synapses on the vessels of the primary capillary network. Neuroharmones produced by these neurosecretory cells move along their axons to the medial eminence. Here they accumulate and then enter the capillaries of the primary vascular network through axovascular synapses. The latter gather in portal veins, which are directed along the pituitary stalk to the adenohypophysis. Then they break up again and form a secondary capillary network. Sinusoidal capillaries This network is intertwined with trabeculae of secreting adenocytes.
The blood flowing through the veins from the secondary vascular network contains adenohypophyseal hormones, which, through the general blood flow, that is, in a humoral way, regulate the functions of the peripheral endocrine glands.
The neurohypophysis (posterior lobe) develops from the medullary recess, so it is built from neuroglia. Its cells are fusiform or process-shaped pituicytes. The processes of pituicytes are in contact with blood vessels. The posterior lobe includes large bundles of nerve fibers formed by the axons of neurosecretory cells of the paraventricular and supraoptic nuclei of the anterior zone of the hypothalamus. The neurosecretion formed by these cells moves along the axons into the neurohypophysis in the form of secretory drops. Here they settle in the form of storage bodies, or terminals, which are in contact with the capillaries.
Consequently, the hormones of the neurohypophysis - oxytocin and vasopressin - are synthesized not by the structures of the neurohypophysis, but in the paraventricular and supraoptic nuclei. Then, as mentioned above, hormones travel along nerve fibers to the neurohypophysis, where they accumulate and from where they enter the bloodstream. Therefore, the neurohypophysis and hypothalamus are closely connected and form a single hypothalamic-neurohypophyseal system.
Oxytocin stimulates function smooth muscles uterus, thereby promoting the secretion of uterine gland secretions; during childbirth causes strong contractions muscularis propria uterine walls; regulates the contraction of the muscle elements of the mammary gland.
Vasopressin narrows the lumen of blood vessels and increases blood pressure; adjustable water exchange, as it affects the reabsorption (reabsorption) of water in the kidney tubules.
