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The Endocrine System
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System Overview Includes cells, tissues, and organs that secrete hormones directly into the body fluids Endocrine vs. exocrine
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Functions of Hormones Help regulate metabolic processes
Control the rates of some chemical reactions Aid in the transport of substances across membranes Help regulate water and electrolyte balances Play vital roles in reproduction, growth, and development
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What is a Hormone? A biochemical secreted by a cell to affect the functions of another cell Action of a hormone is restricted to a specific target cell that has protein receptors for the hormone
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Steroid Hormones Fat soluble Diffuse into cells easily
May bind to DNA and activate genes Fast acting
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Nonsteroid Hormones Usually combine with cell membrane receptors
Binding stimulates activity site of receptor (hormone is first messenger) second messengers inside cell trigger cell action
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Prostaglandins Not really hormones, but behave similarly
Affect only the organ where they are produced Present in very small quantities, not stored, and rapidly inactivated
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Control of Hormone Secretions
Hypothalamus Controls the anterior pituitary gland’s release of hormones that stimulate other endocrine glands Nervous system Stimulates some glands directly Some glands respond directly to changes in the internal environment
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Hormone Regulation
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Major Endocrine Glands and Their Hormones
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Pituitary Gland Located at the base of the brain
Attaches to the hypothalamus by means of the infundibulum Anterior and posterior lobes
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Anterior Pituitary Gland
Dense CT capsule Blocks of glandular epithelium around blood vessels
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Anterior Pituitary Hormones
Growth Hormone (GH) Stimulates most body cells to increase in size and divide Promotes protein synthesis
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Anterior Pituitary Hormones
Thyroid-Stimulating Hormone (TSH) Promotes normal activity and development of the thyroid gland Adrenocorticotropic Hormone (ACTH) Triggers the release of hormones from the adrenal cortex
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Anterior Pituitary Hormones
Follicle-Stimulating Hormone (FSH) Stimulates gamete production in males and females Stimulates maturation of ovarian follicles and eggs in females Luteinizing Hormone (LH) Promotes production of gonadal hormones In females, triggers ovulation and stimulates maturation of ovarian follicles and eggs
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Anterior Pituitary Hormones
Prolactin (PRL) Stimulates milk production in the breasts Enhances testosterone production ?
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Posterior Pituitary Gland
Consists mostly of nerve fibers and neuroglia Closely associated with the hypothalamus
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Posterior Pituitary Hormones
Oxytocin (OT) Stimulates contraction of uterine muscles Triggers “letdown” of breast milk “Cuddle hormone” ?
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Posterior Pituitary Hormones
Antidiuretic Hormone (ADH) Inhibits urine formation in the kidneys Stimulates constriction of blood vessels Released in response to increased blood solute concentration, low blood pressure, some drugs (nicotine, morphine) Inhibited by alcohol and excessive water consumption
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Thyroid Gland Highly vascular Two lobes connected by isthmus
Located below larynx Secretory parts are follicles filled with colloid CT capsule
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Thyroid Hormones Thryoxine (T4) and Triiodothyronine (T3)
Collectively known as thyroid hormone Increases metabolic rate and body heat production Regulates tissue growth
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Thyroid Disorders
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Thyroid Hormones Calcitonin Lowers blood calcium Inhibits osteoclasts
Stimulates osteoblasts
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Parathyroid Glands 4 small glands on posterior of thyroid gland
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Parathyroid Hormone Parathyroid Hormone (PTH) Raises blood calcium
Stimulates osteoclasts Triggers reabsorption of calcium in urine in kidneys Increases intestinal absorption of calcium from food
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Adrenal Glands Located on top of kidneys Embedded in adipose
Adrenal cortex Outer portion of epithelial cells organized into layers Adrenal medulla Consists of modified neurons around blood vessels and nerves of the sympathetic nervous system
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Adrenal Cortex Hormones
Aldosterone Zona glomerulosa Reduces excretion of sodium from kidneys Increases reabsorption of sodium from urine, perspiration, saliva, and gastric juice Increases excretion of potassium Increases water retention
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Adrenal Cortex Hormones
Cortisol Zona fasciculata Helps maintain blood glucose concentration between meals
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Adrenal Cortex Hormones
Androgens Zona reticularis Supplements sex hormones produced by gonads ?
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Adrenal Medulla Hormones
Epinephrine and Norepinephrine Produce short term stress response Increase heart rate, blood pressure, and metabolic rate Dilation of bronchioles Trigger liver to release glucose into bloodstream
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Pancreas Mixed gland Located behind stomach
Islets of Langerhans – masses of endocrine cells amongst acinar (exocrine) cells
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Pancreas Hormones Insulin Glucagon
Produced by beta cells (stain purple) Decreases blood glucose concentration Enhances absorption of glucose into cells for energy use and storage Glucagon Produced by alpha cells (stain pink) Stimulates liver to release glucose from glycogen 1 molecule triggers the release of 100 million glucose molecules into the blood
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Ovaries Female gonads Produce estrogen and progesterone:
Stimulate maturation of the female reproductive organs and appearance of secondary sexual characteristics More info later…
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Testes Male gonads Produce testosterone: More info later…
Stimulates maturation of the male reproductive organs and the appearance of male secondary sexual characterisics Increases sex drive Promotes normal sperm production More info later…
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Pineal Gland Located between cerebral hemispheres Attached to thalamus
Releases melatonin: Released in response to light Helps regulate circadian rhythms ?
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Thymus Gland Located between the lungs posterior to the sternum
Butterfly-shaped Diminishes during adulthood Produces thymosin: Essential for the normal development of T cells and the immune response More info later…
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Minor Endocrine Glands
Hormone Hormone Actions Heart Atrial Natriuretic Peptide (ANP) Reduces blood volume, blood pressure, and blood Na concentration; Increase urine production in kidneys Stomach Gastrin Triggers release of HCl in stomach Serotonin Stimulates contraction of stomach muscles
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Minor Endocrine Glands
Small Intestine Secretin Triggers release of digestive enzymes from the liver and pancreas; Inhibits stomach secretions Cholecystokinin Stimulates release of pancreatic juice from pancreas; Stimulates release of bile stored in gallbladder Kidney Erythropoietin Increases RBC production in bone marrow Uterus and Placenta Human Chorionic Gonadotropin (hCG) Influences the course of pregnancy
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Minor Endocrine Glands
Epidermis Cholecalciferol Inactive form of vitamin D, Activated by UV, Triggers absorption of Ca in intestines Adipose Tissue Leptin Suppresses appetite
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STRESS!!! Stressor hypothalamus stress response
Physical stressors – extreme temperature, decreased oxygen, infection, injury, prolonged heavy exercise, loud sounds Psychological stressors – thoughts of real or imagined dangers, personal losses, unpleasant social interactions, feelings of fear, anger, grief, anxiety, depression, guilt Stress may even be caused by a pleasant stimulus
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Responses to Stress Blood glucose increases Heart rate increases
Blood pressure rises Breathing rate increases Air passages dilate Blood flow redistributed (away from digestive organs to muscles)
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