Anatomy & Physiology II - Endocrine System PDF

ANATOMY & PHYSIOLOGY II Eng Razaz Salih ENDOCRINE SYSTEM Part II Lecture (3) THE ADRENAL GLANDS  THE ADRENAL GLANDS The paired adrenal (suprarenal) glands lie superior to the kidneys enc...

ANATOMY & PHYSIOLOGY II Eng Razaz Salih ENDOCRINE SYSTEM Part II Lecture (3) THE ADRENAL GLANDS  THE ADRENAL GLANDS The paired adrenal (suprarenal) glands lie superior to the kidneys enclosed within the renal fascia. They are about 4 cm long and 3 cm thick. glands are composed of two parts which have different structures and functions. The outer part is the cortex and the inner part the medulla. The adrenal cortex is essential to life but the medulla is not.  glands are composed of two parts which have different structures and functions. The outer part is the cortex and the inner part the medulla. The adrenal cortex is essential to life but the medulla is not.  HORMONES OF THE ADRENAL GLAND Adrenal cortex: o Cortisol o Corticosterone o Cortisone o Aldosterone o Androgens Adrenal medulla: o Adrenaline (Epinephrine) o Nor-adrenaline (Nor- epinephrine)  ADRENAL CORTEX The adrenal cortex produces three groups of steroid hormones from cholesterol. They are collectively called adrenocorticocoids (corticosteroids). The groups are: ❖ Glucocorticoids ❖ Mineralocorticoids ❖ Sex hormones (androgens) The hormones in each group have different characteristic actions but as they are structurally similar their actions may overlap  GLUCO-CORTI-COIDS Cortisol (hydrocortisone) is the main glucocorticoid but small amounts of corticosterone and cortisone are also produced. Commonly these are collectively known as „steroids‟; they are essential for life, regulating metabolism and responses to stress. It is stimulated by ACTH from the anterior pituitary and by stress. Glucocorticosteroids having a anti-inflammatory actions.  MINERALO-CORTI-COIDS (ALDOSTERONE) Aldosterone is the main mineralocorticoid. It is involved in maintaining water and electrolyte balance. Through a negative feedback system it stimulates the reabsorption of sodium (Na+) by the renal tubules and excretion of potassium (K+) in the urine. Sodium reabsorption is also accompanied by retention of water and therefore aldosterone is involved in the regulation of blood volume and blood pressure too. Blood potassium levels regulate aldosterone secretion by the adrenal cortex. When blood potassium levels rise, more aldosterone is secreted. Low blood potassium has the opposite effect. Angiotensin also stimulates the release of aldosterone (as shown below).  MINERALO-CORTI-COIDS Renin–angiotensin–aldosterone System When renal blood flow is reduced or blood sodium levels fall, the enzyme renin is secreted by kidney cells. Renin converts the plasma protein angiotensinogen, produced by the liver, to angiotensin 1. Angiotensin converting enzyme (ACE), formed in small quantities in the lungs, proximal kidney tubules and other tissues, converts angiotensin 1 to angiotensin 2, which stimulates secretion of aldosterone. Angiotensin 2 causes vasoconstriction and increases blood pressure closing the negative feedback loop  SEX HORMONES Sex hormones secreted by the adrenal cortex are mainly androgens (male sex hormones) although the amounts produced are insignificant compared with those secreted by the testes and ovaries in late puberty and adulthood  ADRENAL MEDULLA The medulla is completely surrounded by the adrenal cortex. It develops from nervous tissue in the embryo and is part of the sympathetic nervous system. When stimulated by extensive sympathetic nerve supply, the glands release the hormones adrenaline (epinephrine, 80%) and noradrenaline (norepinephrine, 20%).  Adrenaline (Epinephrine) And Noradrenaline (Norepinephrine) Noradrenaline is the postganglionic neurotransmitter of the sympathetic division of the autonomic nervous system Adrenaline and some noradrenaline are released into the blood from the adrenal medulla during stimulation of the sympathetic nervous system. The action of these hormones prolongs and augments stimulation of the sympathetic nervous system. THE PANCREAS  The pancreas is classified as both and THE PANCREAS endocrine organ and an exocrine organ, it will also be discussed again with the digestive system. There are three main types of cells in the pancreatic islets: 1. (alpha) cells, which secrete glucagon 2. (beta) cells, which are the most numerous, secrete insulin 3. (delta) cells, which secrete somatostatin (GHRIH)  THE PANCREAS The normal blood glucose level is between 3.5 and 8 mmol/litre (63 to 144 mg/100 mL). Blood glucose levels are controlled mainly by the opposing actions of insulin and glucagon: glucagon increases blood glucose levels insulin reduces blood glucose levels.  THE PANCREAS HORMONES Insulin: Its main function is to lower raised blood nutrient levels, not only glucose but also amino acids and fatty acids. These effects are described as anabolic, i.e. they promote storage of nutrients. When nutrients, especially glucose, are in excess of immediate needs insulin promotes their storage  THE PANCREAS HORMONES Glucagon: Glucagon increases blood glucose levels by stimulating: A. conversion of glycogen to glucose in the liver and skeletal muscles (glycogenolysis) B. Secretion of glucagon is stimulated by low blood glucose levels and exercise and decreased by somatostatin and insulin.  THE PANCREAS HORMONES Somatostatin (GHRIH): This hormone, also produced by the hypothalamus, inhibits the secretion of both insulin and glucagon in addition to inhibiting the secretion of GH from the anterior pituitary PINEAL GLAND  PINEAL GLAND The pineal gland is a small endocrine gland in the brain of most vertebrates. The pineal gland is about 10 mm long, reddish brown in colour and surrounded by a capsule. The gland tends to atrophy after puberty and may become calcified in later life  PINEAL GLAND HORMONE Melatonin: The pineal gland secretes melatonin, which is thought to promote sleepiness and help regulate the body‟s biological clock. THE THYMUS GLAND  THE THYMUS GLAND Thymus is located in the anterior part of the upper mediastinum At birth it weighs 10-12 g During childhood and adolescence 20- 30 g During old age it weighs 3-6 g  THE THYMUS HORMONES Thymosin: Hormones produced by the thymus gland are thymosin= These hormones promote the proliferation and maturation of T cells (white blood cells which destroy microbes and foreign substances). Thymic hormones may also help to retard the aging process. THE OVARIES AND TESTES  THE OVARIES AND TESTES The ovaries and testes are paired oval organs referred to as gonads.  THE OVARIES The ovaries are the female gonads, located in the pelvic cavity. They secrete estrogens and progesterone, which are: 1. responsible for the development and maintenance of female sexual characteristics 2. regulating the female reproductive system [in conjunction with gonadotropic hormones from the pituitary gland]). The ovaries also produce relaxin, which soften connective tissues in preparation for childbirth.  THE TESTES The testes are the male gonads, located in the scrotum. They secrete: 1. Testosterone, which is responsible for male sexual characteristics 2. Inhibin, which controls sperm production by inhibiting follicle stimulating hormone.