Endocrine System Lecture Overview

• The Endocrine System is a specialized system consisting of ductless glands and neurosecretory cells that secrete hormones into the bloodstream.

• Hormones are biologically active chemical messengers that interact with distant target cells, leading to specific responses in terms of metabolism, growth, or reproduction.

• The Endocrine System is one of the body's two major regulatory systems, controlling important functions such as cellular metabolism, water and electrolyte balance, cell growth, development, and reproduction, and helping the body cope with stressful situations.

• Hormones can be classified into several categories based on their chemical structure, including amines, amino acid derivatives, polypeptides, proteins, glycoproteins, steroids, and hydrophilic vs lipophilic hormones.

• Hormones are synthesized through either a vesicle-mediated pathway or a non-vesicle-mediated pathway, and are transported in the bloodstream either free and unbound or bound to carrier proteins.

• The secretion of hormones is controlled by various factors, including timing and pattern (pulsatile or cyclical, diurnal or circadian rhythm), negative feedback, and end-product inhibition.

• Hormones produce their effects on target cells by interacting with specific receptors, which are linked to specific effector systems in the cell, and can be classified into two broad types: cell surface receptors and intracellular or nuclear receptors.

• Endocrine disorders can result from hyposecretion, hypersecretion, or abnormal target cell responsiveness, leading to a variety of health issues.

• The Endocrine System is divided into two broad categories: the Central Endocrine Glands (hypothalamus, pituitary gland, pineal gland) and the Peripheral Endocrine Glands (thyroid glands, adrenal glands, endocrine pancreas, parathyroid glands, gonads).

• The Hypothalamus and Pituitary Gland are located in the diencephalon and function cooperatively as the "master regulators" of the endocrine system, controlling critical homeostatic and metabolic functions through the hypophyseal portal system and the hypothalamo-hypophyseal nerve tract.

• The Hypothalamus is the brain's coordinating center for endocrine, behavioral, and autonomic nervous system function, acting as a neuroendocrine transducer or bridge that converts electrical signals into chemical messages and releases hormones to control pituitary secretions.

• Hypothalamic hormones regulate anterior pituitary secretions through stimulatory and inhibitory hormones, including growth hormone-releasing hormone (GHRH), thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), somatostatin, and dopamine.

• Dr. Gabriel Boachie-Ansah teaches MPharm PHA112 The Endocrine System at the University of Sunderland. He can be contacted at [email protected] or ext. 2617.

• In Week 16, the focus is on Anterior Pituitary Hormones and the Endocrine System.

Anterior Pituitary Hormones:

• Thyroid-stimulating hormone (TSH):
• Promotes vascularization and growth of the thyroid gland.
• Stimulates secretion of thyroid hormones.
• Stimulated by TRH from hypothalamus.
• Adrenocorticotropic hormone (ACTH):
• Controls growth of the adrenal cortex.
• Stimulates secretion of cortisol by the adrenal cortex.
• Stimulated by CRH from hypothalamus.
• Follicle-stimulating hormone (FSH):
• Stimulates growth and development of ovarian follicles (F) and sperm production (M).
• Promotes ovarian secretion of estrogen (F).
• Required for sperm production (M).
• Stimulated by GnRH from hypothalamus.
• Luteinizing hormone (LH):
• Responsible for ovulation and development of the corpus luteum (F).
• Regulates ovarian secretion of sex hormones (F).
• Stimulates testes to secrete testosterone (M).
• Stimulated by GnRH from hypothalamus.
• Prolactin (PRL):
• Enhances breast development and milk production (F).
• Secretion inhibited by DA from hypothalamus.

Posterior Pituitary Hormones:

• Vasopressin (ADH):
• Regulates urinary water loss and water balance in the body.
• Promotes renal water reabsorption.
• Regulates plasma volume and osmotic pressure.
• Oxytocin:
• Stimulates uterine contraction during childbirth and milk ejection during breast-feeding.
• Secretion stimulated by birth canal and breast suckling reflexes.

The Pineal Gland:

• Located in the diencephalon.
• Tiny, pine cone-shaped gland.
• Secretes melatonin, the hormone of darkness.
• Production stimulated by the suprachiasmatic nucleus (SCN), the body's master biological clock.
• Main functions: synchronizes body's circadian rhythms with the 24-hr day-night cycle, promotes sleep, and influences reproductive activity (onset of puberty).

The Thyroid Gland:

• Two lobes of endocrine tissue joined in the middle by a narrow strip of gland (isthmus).

• Consists of two distinct secretory cell types, follicular cells and parafollicular or C cells.

• Follicular cells secrete two iodine-containing hormones, Tetra-iodothyronine (T4 or thyroxine) and Tri-iodothyronine (T3).

• Parafollicular or C cells secrete calcitonin (peptide hormone).

• Located in the neck, just below the larynx.

• The MPharm Programme in Week 16 focuses on the endocrine system, specifically the adrenocortical hormones and the endocrine pancreas.

• The adrenocortical hormones include mineralocorticoids (aldosterone) and glucocorticoids (cortisol).

• Mineralocorticoids are essential for maintaining Na+ and K+ balance and ECF volume, and promote Na+ retention and K+ excretion.

• The principal site of action is the distal and collecting tubules of the kidney.

• Secretion is regulated by angiotensin II, elevated serum K+ levels, and ACTH (minor).

• Glucocorticoids are involved in regulating carbohydrate, protein, and fat metabolism.

• They promote gluconeogenesis, cellular glucose uptake and utilization, protein synthesis and catabolism, and lipolysis.

• Cortisol plays a key role in adaptation to stress and exerts anti-inflammatory and immunosuppressive effects.

• The adrenocortical hormones also include sex hormones, specifically 'androgenic' DHEA, which supplement sex hormones secreted by the gonads.

• The adrenal medulla is a modified sympathetic postganglionic neuron that secretes adrenaline, noradrenaline, and dopamine.

• Its main functions include reinforcing the "fight-or-flight" response and maintaining arterial blood pressure by regulating heart rate, cardiac output, respiratory rate, and glycogenolysis and lipolysis.

• The endocrine pancreas consists of clusters or 'islands' of secretory cells, called islets of Langerhans.

• It comprises three types of secretory cells: alpha (glucagon), beta (insulin), and delta (somatostatin).

• Insulin is an important anabolic hormone that regulates fuel metabolism and promotes cellular uptake and storage of glucose, fatty acids, and amino acids.

• It enhances their conversion into glycogen, triglycerides, and proteins through glycogenesis, glycogenolysis, and gluconeogenesis, triglyceride synthesis, and lipolysis, and protein synthesis and degradation.

• Glucagon is generally opposing to insulin and mobilizes energy-rich molecules from storage sites into the bloodstream, raising blood glucose levels.

• It induces hepatic glucose production, glycogenolysis, and gluconeogenesis, and lipolysis and ketogenesis, and triglyceride synthesis, and protein synthesis and degradation.

• Parathyroid hormone (PTH) is a single most important regulator of blood Ca++ levels and raises plasma Ca++ levels through bone resorption, renal reabsorption, and the activation of vitamin D, which enhances intestinal absorption of Ca++.

• Vitamin D is the second most important regulator of blood Ca++ levels and controls plasma Ca++ levels through intestinal absorption, bone resorption, and the synthesis of PTH.

• Calcitonin is a hormone secreted by parafollicular or C cells of the thyroid gland and exerts opposite effects to PTH, lowering plasma Ca++ levels through bone resorption and renal reabsorption.

• Its secretion is regulated by blood Ca++ levels.

• PTH and vitamin D have complementary interactions, with vitamin D enhancing PTH synthesis and PTH regulating vitamin D activation and secretion.

• The Gastro-intestinal (GI) System is a group of organs that work together to break down ingested food into smaller, absorbable nutrient molecules.

• The main functions of the GI System include digesting food into smaller units, absorbing nutrients, and making preformed organic nutrient molecules available to the body.

• The GI System performs five basic processes: motility, secretion, digestion, absorption, and storage & elimination of indigestible food.

• Motility refers to muscular contractions that mix and move the contents of the digestive tract. There are two types of digestive motility: propulsive movements that push contents through the digestive tract, and mixing movements that mix food with digestive juices and promote absorption.

• Secretion refers to the release of digestive juices in the GI tract in response to specific neural or hormonal stimulation. These secretions consist of water, electrolytes, and specific organic constituents, including enzymes, mucus, and hormones.

• Digestion is the biochemical breakdown of complex foodstuffs into smaller, absorbable units. This process is accomplished by enzyme-mediated hydrolysis of complex foodstuffs into monosaccharides (carbohydrates), amino acids (proteins), and glycerol and fatty acids (fats).

• Absorption is the transfer of small digested units, along with water, vitamins, and electrolytes, from the GI tract into the blood or lymph. This process occurs largely and most completely in the small intestine.

• The GI System is composed of the alimentary canal, which is a long, continuous hollow tube stretching from the mouth to the anus, and accessory organs and glands, such as the salivary glands, liver, and pancreas.

• The alimentary canal is divided into three main parts: the upper part, which serves as the food intake source and receptacle site for initial digestive processes; the middle part, which is the site of main digestive and absorptive processes; and the lower part, which serves as the storage channel for efficient elimination of waste.

• The wall structure of the alimentary canal consists of four layers: the mucosa, submucosa, muscularis externa, and serosa. The mucosa is the innermost layer and serves as a protective barrier against pathogens, secretes mucus, digestive enzymes, and hormones, and absorbs digested nutrients.

• The GI System is regulated by both intrinsic and extrinsic factors, which include interstitial cells of Cajal (pacemaker cells), intrinsic nerve plexuses, extrinsic nerves, and gastrointestinal hormones. These factors mediate the processes of digestion and absorption through complex regulatory mechanisms.

• Digestive processes occur from the mouth to the stomach. Mastication, or chewing, aids in the mechanical breakdown of larger food units and mixes food with saliva, which contains salivary amylase and starts the process of partial digestion of starch. Deglutition, or swallowing, is the process of moving a bolus of food through the pharynx and into the esophagus.

• The text is about the human body's anatomy, specifically focusing on body cavities, planes, and membranes.

• There are three main body cavities: cranial, thoracic, and abdominopelvic.

• The cranial cavity houses the brain, while the vertebral canal contains the spinal cord.

• The thoracic cavity, also called the chest cavity, is formed by the ribs, muscles of the chest, sternum, and vertebral column. It has two fluid-filled spaces: the pleural cavities, which surround the lungs, and the pericardial cavity, which surrounds the heart.

• The abdominopelvic cavity extends from the diaphragm to the groin and is divided into two portions: the abdominal cavity and the pelvic cavity. The abdominal cavity contains the stomach, spleen, liver, gallbladder, small and large intestines, while the pelvic cavity houses the urinary bladder, internal organs of the reproductive system, and portions of the large intestine.

• The body cavities are lined by serous membranes, including the pleura, pericardium, and peritoneum. The visceral layer covers the organs within the cavities, while the parietal layer lines the walls of the cavities.

• There are several planes used to describe the body's anatomy, including the sagittal, frontal or coronal, and oblique planes. These planes help to describe the location and orientation of various structures within the body.

• There are also several important terms related to the body cavities and their subdivisions, including the dorsal body cavity, superior and inferior mediastinum, and the diaphragm.

• The body cavities and their subdivisions are further delineated by nine regions or quadrants, including the right and left hypochondriac, epigastric, hypogastric (pubic), right and left lumbar, and umbilical regions. These regions help to identify the location of various organs within the body.

• Nephrons come in two types: those with short loops of Henle (no thin segments in their ascending limbs) and those with long loops (thin and thick segments in their ascending limbs).

• The former receive blood supply from peritubular capillaries, while the latter receive it from vasa recta.

• Distal convoluted tubules of several nephrons empty into a single collecting duct.

• Collecting ducts unite and converge into several hundred large papillary ducts which drain into minor and major calyces, renal pelvis, and ureters.

• Glomerular filtration involves the filtration of 180 L of plasma daily, resulting in 178-179 L being returned to blood and 1-2 L in urine.

• The filtration pressure is maintained at 10 mmHg.

• Glomerular filtration is regulated by two hormones: angiotensin II constricts both afferent and efferent arterioles, while atrial natriuretic peptide (ANP) causes the glomerulus to relax and increase filtration.

• Sodium and other ions are reabsorbed in the proximal convoluted tubule through active transport, symporters, and secondary active transport.

• The thick ascending limb of the loop of Henle reabsorbs 20-30% of filtered sodium, potassium, and chloride; 35% of filtered bicarbonate; and variable amounts of calcium and magnesium.

• The distal convoluted tubule and collecting duct reabsorb sodium and secrete potassium.

• Five hormones, including angiotensin II, antidiuretic hormone (ADH), aldosterone, atrial natriuretic peptide (ANP), and parathyroid hormone (PTH), affect sodium, chloride, calcium, and water reabsorption and potassium secretion in the renal tubules, maintaining homeostasis.

• ADH is released by the posterior pituitary and increases the water permeability of principal cells in the collecting duct and distal convoluted tubule, while in its absence, the cells are almost impermeable to water.

• PTH is released by the parathyroid gland and stimulates cells in the early distal convoluted tubule to reabsorb calcium, inhibiting phosphate reabsorption in the proximal convoluted tubule to promote phosphate excretion.

• The uterine tubes, also known as Fallopian tubes or oviducts, transport a secondary oocyte from the ovary to the uterus, where fertilization usually occurs.

• The uterus is the site of implantation of the fertilized ovum, development of the fetus during pregnancy, and labor.

• The vagina is the passageway for intercourse and childbirth, and is the site of menstruation.

• The ovaries are paired glands located in the pelvic cavity, each with a structure consisting of a germinal epithelium, tunica albuginea, ovarian cortex, and follicles.

• Oogenesis, the process of forming gametes in the ovaries, involves several stages, including the formation of primary oocytes during fetal development, maturation of a few into secondary oocytes each month, and ovulation of one secondary oocyte from a mature follicle.

• Ovulation is the process by which a mature follicle ruptures, releasing a secondary oocyte, and is followed by the formation of the corpus luteum, which produces hormones until it degenerates.

• The oviducts are narrow tubes that extend from the ovary to the uterus, with various structures, including the infundibulum, ampulla, isthmus, and fimbriae, which help to move the secondary oocyte into the tube and towards the uterus.

• The uterus is a muscular organ that is responsible for maintaining the fetus during development and expelling it at the end of pregnancy, and is about 3 inches long, 2 inches wide, and 1 inch thick.

• The vagina is a fibrous muscular canal that extends from the exterior to the cervix, is about 10cm long, and is lined with mucous membrane. It serves as a passageway for sperm, the delivery of the baby, and menstrual flow.

• The external genitalia of the female, collectively referred to as the vulva, includes the mons pubis, labia minora and labia majora, and the clitoris.

• The mammary glands are modified sudoriferous glands that secrete milk through a process called lactation, which is associated with pregnancy and childbirth. They are internally composed of lobes, lobules, and alveoli.

• The process of lactation involves the synthesis, secretion, and ejection of milk from the alveoli, and is stimulated by the hormones oestrogen, progesterone, and prolactin.

• The dominant female sex hormones are oestrogen and progesterone.

Note: The above summary is based on the provided text and is not meant to be an exhaustive or definitive summary. It is intended to capture the key facts, figures, and entities mentioned in the text.