Endocrine System PDF

ENDOCRINE SYSTEM Prepared by: Shiela Mae G. Bolambot, 1 DVM Definition of Terms Endocrinology – branch of physiology which deals with the study of endocrine glands and their associated chemical messengers that regulate the activity of other cells of the body....

ENDOCRINE SYSTEM Prepared by: Shiela Mae G. Bolambot, 1 DVM Definition of Terms Endocrinology – branch of physiology which deals with the study of endocrine glands and their associated chemical messengers that regulate the activity of other cells of the body. 2 Endocrine system part of the regulatory system of the body and works in conjunction with the nervous system. Purpose Homeostasis: maintaining the body’s internal environment 3 Definition of Terms Hormone – comes from the Greek word “hormon” which means “to arouse or to stimulate” ; chemical substances secreted by endocrine glands that regulates activity of other cells in the body. 5 Hormone Hormones appear to regulate rather than initiate reactions Hormones are effective in biocatalytic amounts Hormones are not secreted in uniform rates Hormones are inactivated rapidly either at the site where it exerts its effect or at some other glands and organs; and Hormones are transported through the circulatory system or blood stream 6 Hypothalamus Controls the pituitary gland Produces chemical signals Releasing stimulating hormones Releasing inhibitory hormones Helps regulate metabolism heart rate energy level body temperature thirst 14 Pituitary Gland Also known as the Hypophysis, and also the “Master Gland” Divided into two lobes Anterior Pituitary Gland Posterior Pituitary Gland 15 Hormones of the Anterior Pituitary Anterior Pituitary Gland (Adenohypophysis) Hormones Secreted: Growth Hormone Adrenocorticotropic Hormone Thyroid-Stimulating Hormone Gonadotropic Hormones Prolactin 17 Growth Hormone (GH) also known as somatotropic hormone (STH) or Somatotropin Controlling the rate of growth at the epiphyses of Somatome the bones dins Being involved in protein production from amino acids Regulating the use of energy during periods of poor food supply. Insufficient secretion of growth hormone in a young animal causes it to be underdeveloped- a condition known as PITUITARY DWARFISM. Overproduction in a young animal, before the epiphyses close, results in a giant animal 18 Adrenocorticotropic Hormone (ACTH) -stimulates the adrenal cortex which is responsible for secreting several hormones. Thyroid-Stimulating Hormone (TSH) -stimulates the synthesis of colloid by thyroid gland cells and stimulates the release of thyroid hormone. 19 Gonadotropic Hormones Follicle stimulating hormone (FSH) - Stimulates oogenesis and spermatogenesis in the female and male, respectively. Luteinizing hormone (LH) In the female: - LH assists ovulation and development of a functioning corpus luteum In the male - it stimulates the secretion of testosterone. Prolactin - helps to initiate and maintain lactation after pregnancy. 20 Hormones of the Posterior Pituitary Posterior Pituitary Gland (Neurohypophysis) Hormones Secreted: contains the terminal axons from two pairs of Antidiuretic Hormone nuclei: Oxytocin Supraoptic nuclei: synthesize antidiuretic hormone Paraventricular nuclei: synthesize oxytocin Which are transported to the axon terminals in the pos. pit., and stored in secretory granules until released. If in need for each of the stored hormones, it causes the release of the hormone. 22 Antidiuretic Hormone (ADH) - also known as Vasopressin When an animal is given an overload of water, a period of diuresis (increased output of dilute urine) occurs. Diuresis can be prevented by Antidiuretic Hormone (ADH). The target cells of the secreted ADH are the: collecting tubules and the collecting ducts of the kidney ADH is therefore important for water conservation by animals. What circumstances you need to conserve water? Antidiuretic Hormone (ADH) Antidiuretic Hormone (ADH) Oxytocin -released as a result of neuroendocrine reflexes. Adrenal Gland small, paired structures that lie immediately cranial to the kidneys Hormones of Adrenal cortex: The hormones produced are known as steroids Glucocorticoids (cortisol ) Mineralocorticoids (aldosterone) Hormones of Adrenal medulla: The hormones produced are known as catecholamines Epinephrine (adrenaline) Norepinephrine (noradrenaline) 27 Adrenal cortex: Glucocorticoids (CORTISOL) secreted by the zona fasciculata of the adrenal cortex. Their secretion is regulated by ACTH from the anterior pituitary. In the normal animal, they are present in low levels but increase in response to stress. Adaptation to various stresses in order to maintain homeostasis Function: They increase blood glucose levels by reducing glucose uptake by the cells, increasing the conversion of amino acids to glucose in the liver (a process known as gluconeogenesis ) and mobilizing fatty acids from the adipose tissue ready for conversion to glucose. When present in large quantities, they depress the inflammatory reaction, which delays healing and repair. This property is used therapeutically to reduce swelling and inflammation. 28 Adrenal cortex: Mineralocorticoids (ALDOSTERONE) secreted by the zona glomerulosa of the adrenal cortex. Enhance sodium reabsorption and potassium excretion. This acts on the distal convoluted tubule of the kidney where it regulates acid-base balance of the plasma and ECF by excretion of H+ ions and also controls the excretion of Na+ and K+ ions. 29 Adrenal medulla: Epinephrine and Norepinephrine These hormones prepare the body for emergency action. and are controlled by the sympathetic nervous system. “FIGHT–FRIGHT–FLIGHT” Raise blood glucose levels by the breakdown of glycogen stored in the liver- glycogenolysis. Increase the heart rate and the rate and depth of respiration Dilate the blood vessels of the skeletal muscles Decrease the activity of the gastrointestinal tract and the bladder. 30  Disease Association ADDISON DISEASE CUSHING’S DISEASE caused by under secretion of glucocorticoids and mineralocorticoids or hypoadrenocorticalism. caused by oversecretion of glucocorticoids The clinical signs: or hyperadrenocorticalism. The clinical signs include: vomiting polydipsia, Diarrhea polyuria, Anorexia polyphagia, bilateral symmetrical alopecia, lethargy muscle Dehydration wasting and a potbelly. bradycardia Collapse (eventually) Thyroid Gland located on the trachea, just caudal to the larynx. The thyroid gland is composed of numerous follicles and filled with a fluid known as colloid. Hormones: Tetraidothyronine or Thyroxine (T4) Triiodothyronine (T3) Calcitonin 32 HOW IS T3 AND T4 SYNTHSIZED? 33 HOW IS T3 AND T4 SYNTHSIZED? 34 Thyroxine (T4) and How to regulate secretion of thyroid Triiodothyronine (T3) hormones? Secretion of thyrotropin Decreased levels of releasing hormone thyroid hormones (TRH) into the hypophysioportal circulation TSH secretion is followed by Thyrotrope Absorption increased cells of the into the thyroid gland anterior blood, and activity, pituitary are transport to including the thereby cells release of T3 stimulated by and T4 TRH to secrete TSH 35 Thyroxine (T4) and Triiodothyronine (T3) Functions: ability to increase internal heat, thereby increasing the rate of oxygen consumption secondary to increased protein synthesis stimulated by thyroid hormones. stimulate the metabolic activities of most tissues of the body except for the brain, lungs, retina, testes, and spleen. The ability to increase metabolic activity and oxygen consumption is partly a result of the stimulation or activation of some key enzymes, including alpha-glycerophosphate dehydrogenase, hexokinase, diphosphoglycerate mutase, and cytochromes b and c. The lipolytic effect of epinephrine is also markedly potentiated by thyroid hormones (during excitement and Anxiety). 36 Thyroid gland enlarges because of colloid accumulation, a condition known as ? GOITER is rarely seen in the domestic animals. 37  Thyroid gland enlargement can be caused by Hypothyroidism Hyperthyroidism (e.g., iodine deficiency) (e.g., increased thyroxine - Is more common in dogs. demands, tumor) - In young animals, hypothyroidism causes DWARFISM (stunted growth). - is more common in old cats. The affected animal is thin, active, often aggressive, has - In older animals, the condition is a good appetite and a fast heart rate, all due to a raised known as MYXOEDEMA: the dog becomes fat and sluggish, alopecic, the skin feels cold and metabolic rate. clammy and the heart rate slows, all due to a reduced metabolic rate. 38 Calcitonin secreted by parafollicular or C cells. Stimulation for secretion of Function: lowers the levels of blood calcium by decreasing calcitonin is HYPERCALCEMIA the rate of bone resorption. When levels of blood and, to a lesser calcium are high (e.g., if a calcium-rich diet is extent, eaten), calcium is deposited in the bone and acts HYPERMAGNESEM as a reservoir for later use IA. Antagonistic to the action of another hormone associated with calcium homeostasis, Parathyroid Hormone. The latter hormone protects against low plasma concentrations of Ca2+. 39 Parathyroid Glands -are located near or embedded within the thyroid gland. - pairs of bean-like structure. In domestic animals they consist of: -one (pig) - two (dog, cat, ruminant, horse) Hormone: Parathyroid hormone (PTH) 40 Parathyroid hormone or Parathormone (PTH) Secretion is dependent on the levels of calcium in the blood. is known as a hypercalcemic hormone PTH increase plasma calcium levels by: Bone: increase bone resorption and mobilize calcium Kidney: increases calcium reabsorption in proximal renal tubules; increase phosphate excretion GIT: increase gut calcium absorption by promoting formation of 1,25 dihydroxycholecalciferol (Vitamin D3). 41 Compare and contrast the functions of Calcitonin from the thyroid gland and Parathyroid Hormone from the parathyroid gland. 42 Pancreas pinkish lobular gland lying in the loop of the duodenum in the abdominal cavity. It has an exocrine part and an endocrine part. The endocrine secretions are produced by discrete areas of tissue within the exocrine tissue, known as the islets of Langerhans Hormones : Alpha Cells Beta Cells Secretes Glucagon Secretes Insulin 43 Glucagon “hyperglycemic hormone” target tissue: liver elevate blood glucose levels by increasing glycogen breakdown, gluconeogenesis also stimulate lipolysis Insulin “hypoglycemic hormone” lower blood glucose, amino acid and fatty acids promote intracellular conversion of said compounds into storage form (glycogen, proteins and triglycerides) Estrogen Progesterone produced by the walls of the developing ovarian is secreted by the corpus luteum, which follicles. develops Development of germ cells in the ovary from the remaining follicular tissue after the into ripe follicle has follicles  is the result of the secretion of ovulated. FSH from the anterior pituitary gland. The corpus luteum develops as a result of the Oestrogen causes: production of LH from the anterior pituitary gland. behaviour associated with the estrous cycle Progesterone causes: the reproductive tract for pregnancy and prepares the reproductive tract and maintains the pregnancy external genitalia for mating. During pregnancy, progesterone exerts negative feedback on the hypothalamus and exerts negative feedback on the prevents secretion of Ovaries lie one on each side of the dorsal abdominal cavity caudal to the kidneys. At the onset of sexual maturity, the two ovaries become capable of secreting two hormones: Hormones: Estrogen Progesterone 46 Hooray! Let’s review 47 Progesterone is secreted by the corpus luteum. The corpus luteum develops as a result of the production of LH from the anterior pituitary gland. Progesterone causes: Prepare and maintains pregnancy During pregnancy, - progesterone prevents further estrous cycles Development of the mammary glands during pregnancy. In the later stages of pregnancy, the corpus luteum also secretes a hormone known as relaxin. Relaxin causes the sacroiliac and other ligaments around the birth canal to soften and relax in preparation for parturition. The Testes Male mammals possess a pair of testes, which are carried external to the abdominal cavity within the scrotum. At the start of sexual maturity, the testes begin to secrete two hormones: Hormones: Testosterone Estrogen 49 Testosterone produced by the interstitial cells or cells of Leydig in response to the secretion of ICSH from the anterior pituitary gland. Testosterone is responsible for: The development of male characteristics such as penis development, muscle development, size Male behavior patterns, such as sexual drive, aggression, territorial behavior, courtship displays and mating behavior Development of spermatozoa Estrogen is produced in small quantities by the Sertoli cells in the seminiferous tubules of the testes. 50