Hormones PDF

# Hormones ## Male Gonads - The male gonads are the testes, which have two functions: spermatogenesis and secretion of testosterone. - The testes secrete other androgens, but they are produced in smaller amounts. - Testosterone stimulates the development of male reproductive structures and male sec...

# Hormones ## Male Gonads - The male gonads are the testes, which have two functions: spermatogenesis and secretion of testosterone. - The testes secrete other androgens, but they are produced in smaller amounts. - Testosterone stimulates the development of male reproductive structures and male secondary sexual characteristics. ## Female Gonads - The female gonads are ovaries, which have two functions: oogenesis and secretion of the female sex steroid hormones, progesterone, and estrogen. ## Effect of Estrogens on Target Tissues - Maturation and maintenance of uterus, fallopian tubes, cervix, and vagina. - Responsible at puberty for the development of female secondary sex characteristics. - Required for development of the breasts. - Responsible for proliferation and development of ovarian granulosa cells. - Maintenance of pregnancy. - Stimulation of prolactin secretion. ## Effect of Progesterone on Target Tissues - Maintenance of secretory activity of the uterus during the luteal phase. - Development of the breasts. - Maintenance of pregnancy. ## Pancreas - Is a mixed exocrine and endocrine tissue. - The exocrine portion secretes digestive enzymes into the digestive tract lumen. - Between the exocrine cells, about a million islands of endocrine cells known as the islets of Langerhans. - The islets make up about 1% to 2% of the total pancreatic mass. ## Functions of the Pancreatic Islets: - **α-cells:** produce glucagon and make up 25% of the islet mass. Glucagon increases blood glucose levels, increases glycogenolysis, and gluconeogenesis. - **β-cells:** are the site of insulin synthesis and secretion and constitute about 60% of the total islet mass. Insulin decreases blood glucose concentration and promotes glycogenesis. - **δ-cells:** (10% of islet mass) produce somatostatin synthesis, which decreases stomach acid secretion that slows down the digestive process. - **F-cells:** (1% of islet mass) secrete pancreatic polypeptide, which plays a role in reducing appetite and food intake. ## Additional Pancreatic Structures - The remaining 4% of islet mass consists of connective tissue, blood vessels, and nerves. - Parasympathetic, sympathetic, and sensory nerves richly innervate the pancreatic islets, and the respective neurotransmitters and neuropeptides released from their nerve terminals exert important regulatory effects on pancreatic endocrine hormone release. ## Hormones of the Adrenal cortex - **Mineralocorticoids:** regulate ion (sodium and potassium) balance in the blood. Aldosterone is produced in the greatest amounts. - **Glucocorticoides:** help to provide energy for cells by stimulating the increased use of lipids and proteins. Cortisol is the major glucocorticoid hormone. - **Androgens:** have weak androgenic activity. In the testes, they are converted to testosterone, a more potent androgen. ## Hormones of Adrenal Medulla - **Epinephrine and norepinephrine:** have fight and flight response, which increases heart rate, blood pressure, and ventilation. It also dilates the airways, decreases gastrointestinal motility and secretions, and increases blood glucose concentration. ## Adrenal Gland - The adrenal glands lie on top of the kidneys and consist of: - **Adrenal medulla:** core of the gland - **Adrenal cortex:** outer layers surrounding the core. ### Adrenal Cortex Zones - **Zona Glomerulosa:** secretes mineralocorticoids (aldosterone). - **Zona Fasciculata:** constitutes 75% of adrenal cortex. Secretes glucocorticoides (cortisol). - **Zona Reticularis:** secretes androgens. - **Capsule:** surrounds the adrenal gland. ### Functional Differences between Cortex and Medulla - The medulla and cortex act as separate endocrine glands, as they are involved with the synthesis and release of different hormones: - **Medulla:** chromaffin cells secrete **catecholamines** (80% epinephrine and 20% norepinephrine) in response to sympathetic stimulation. - **Cortex:** secretes **corticosteroids**. ## Posterior Pituitary Hormones - **Oxytocin:** - Stimulates powerful uterine contractions, which trigger labor and delivery of an infant. - Stimulates milk ejection in nursing women. - **Note:** Prolactin stimulates the synthesis of breast milk. - **Antidiuretic hormone (ADH):** - Also called vasopressin. - Has two actions: - On the kidney (regulates serum osmolarity). - On vascular smooth muscle (constriction). ## Anterior Pituitary Hormones - **Growth hormone (GH):** - Is secreted by somatotrophes cells. - Is an anabolic hormone that stimulates growth of all body tissues but especially skeletal muscle and bone. - Has effects on protein, carbohydrates, and fat metabolism. ## Thyroid-Stimulating Hormone (TSH) - Is secreted by thyrotrophs cells. - Stimulates thyroid hormone synthesis and secretion. - Synthesis of T3 and T4. ## Prolactin - Is secreted by lactotrophs cells. - Is the major hormone responsible for milk production. - Participates in the development of the breasts. ## Adrenocorticotropic Hormone (ACTH) - Is secreted by corticotrophs. - Stimulates secretion of the hormone cortisol from the adrenal cortex. ## Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) - Are secreted by gonadotrophs cells. - Are called gonadotropins, glycoprotein hormones capable of promoting the growth and function of the gonads: the ovaries and testes. ## Chemistry of Hormones Hormones can be chemically classified into four groups: 1. **Amino acid-derivatives:** Hormones derived from amino acids tyrosine and tryptophan. They include the hormones secreted by the adrenal medulla, thyroid, and pineal glands. 2. **Polypeptides:** Hormones that are chains of amino acids less than 100 amino acids. They include the antidiuretic hormone and insulin. 3. **Glycoproteins:** Hormones that are long polypeptides (containing chains of amino acids more than 100 amino acids) bound to one or more carbohydrate groups. Examples are follicle-stimulating hormone (FSH) and luteinizing hormone (LH). 4. **Steroids:** Hormones that are lipids derived from cholesterol. Steroids are characterized by four interlocking carbohydrate rings. They include the hormones testosterone, estradiol, progesterone, and cortisol. ## Thymus Gland - Located behind the sternum and in front of the lungs, and only active until puberty. - After puberty, the thymus shrinks and becomes replaced by fat. - The hormones of the thymus stimulate the development of disease-fighting cells. ## The Endocrine Brain and Pituitary Gland - **Pineal gland:** a cone-shaped gland located deep in the center of the brain. It produces melatonin, which helps maintain circadian rhythm and regulate reproductive hormones. - **Hypothalamus:** regulates the secretory activity of the pituitary gland in response to other hormones, sensory information, and emotions. - **Pituitary gland:** located at the base of the brain and connected to the hypothalamus by a stalk of tissue called the **infundibulum**. ### Hypothalamic-Pituitary Relationships - The **hypothalamus** releases high concentrations of hypothalamic hormones, delivered to the anterior pituitary by the hypothalamic-hypophysial portal system. - **Posterior pituitary hormones** are synthesized in nerve cell bodies located in hypothalamic nuclei, packaged in secretory granules, and transported down the axons to the posterior pituitary for release into the circulation. ### Pituitary Gland lobes: - **Anterior pituitary gland (adenohypophysis):** secretes growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL). - **Posterior pituitary (neurohypophysis):** secretes vasopressin or antidiuretic hormone (ADH) and oxytocin (OT). ## Thyroid Gland - A butterfly-shaped organ located at the front of the neck. - It is composed of two lobes, left and right, connected by a narrow isthmus. - It weighs 25 grams in adults, with each lobe being about 5 cm long, 3 cm wide, and 2 cm thick, and the isthmus about 1.25 cm in height and width. - Each lobule is composed of 20-40 follicles, lined by epithelial cells that surround colloid (thyroglobulin), which is a stored form of thyroid hormone. - Scattered parafollicular cells lie between the follicles which secrete calcitonin. ## Thyroid Hormones (T3 and T4) - Affect nearly every tissue in the body, influencing metabolism and maturation. ## Calcitonine - Plays a role in reducing the concentration of calcium in the body fluids when calcium levels become elevated. ## Endocrine System ### General Principles - The endocrine system regulates and integrates cellular activity throughout life. - It maintains homeostasis by regulating cellular and organ function and ensuring a constant internal environment. ### Key Functions - Regulation of sodium and water balance and blood volume and pressure. - Regulation of calcium and phosphate balance. - Regulation of energy balance and fuel mobilization, utilization, and storage. - Coordination of the hemodynamic and metabolic counter regulatory responses to stress. - Regulation of reproduction, development, growth, and senescence. ### Components - **Endocrine glands:** ductless glands that secrete hormones into the interstitial space for transportation to the circulation. - **Hormones:** chemical products released from the cell that exert a biological action on a target cell. - **Target organ:** contains cells that express hormone-specific receptors and respond to hormone binding by a demonstrable biological response.