Chapter 16 - The Endocrine System Flashcards
Exocrine Glands
Produce saliva, milk, HCl, for example.
Endocrine Glands
Release hormones into the blood and lymph nodes. Include following glands:
- Pituitary
- Thyroid
- Parathyroid
- Adrenal
- Pineal
- Thymus
- Pancreas
- Gonads
Hormones
Chemical substances secreted by cells. They regulate metabolic funtions
Amino Acid based Hormones
Most of the hormones in the body.
- AA Derivatives: Catecholamines like epinephrine, dopamine, thyroid hormones, and melatonin.
- Peptide Hormones: Ex, ADH, oxytocin, GH, and prolactin
Steroids
Lipid Derivatives. Structurally related to cholesterol.
Eicosanoids
Lipid derivatives, include prostaglandins.
Target Cell Specificity
Hormones only target specific cells which have the correct receptors on their membrane. The hormones then change the activity of the target cell.
Factors Influencing Target Cell Activation
- The blood levels of the hormones.
- The number of receptors on the target cell
- The affinity of the hormone and the receptor
Mechanisms of Hormone Action
- Produce a chance in the plasma membrane permeability or electrical state.
- Synthesize proteins and enzymes
- Produce enzyme activation or deactivation.
- Induce secretion
Second Messenger System
Nearly all water soluble hormones cannot pass through the lipid membrane of a cell so they act through a second messenger. The hormone binds to a receptor on the membrane, which delivers a signal to an enzyme. The activated enzyme is the second messenger which converts ATP to cyclic AMP and this initiates a cascade of chemical reactions
Direct Gene Activation
Lipid soluble hormones, such as steroids, can pass right though the membrane and bind to receptors within the cytoplasm or nucleus. This interacts with chromatin where the hormones bind to the DNA protein and turns on DNA transcription of RNA to direct protein synthesis
Third Messenger
If calcium levels are changed by the second messenger system, it then acts as a third messenger.
Hormone Regulation
Synthesis and release of hormones is regulated by negative feedback where rising hormone levels inhibit further hormone release.
Hormonal Stimuli
Pituitary gland secretes ACTH hormone which stimulates glucocorticoid hormone secretion by the adrenal cortex. Once secreted, glucocorticoid influences various organs. Once the organs are influenced, it exerts a negative feedback on the adrenal cortex inhibiting ACTH production.
Humoral Stimuli
Level change of certain ions and nutrients which stimulates hormone release.
Neural Stimuli
Nerve fibers that actually stimulate hormone release.
Nervous System Control
Stimulus and feedback inhibitions can be moderated by the nervous system. The hypothalamus releases regulatory hormones into the blood to influence the activity of the anterior pituitary glad.
Pituitary Gland
Consists of 2 lobes. The posterior which is a storage area that receives hormones from the hypothalamus. The anterior which is the glandular part, it manufactures and releases 6 hormones. 4 are tropic, and control other endocrine glands, the other 2 on non endocrine targets. All work via second messenger systems.
Growth Hormone
Release by the anterior pituitary. Protein hormone whose main targets are the bones and skeletal muscle. Promotes protein synthesis, use of fats, and conservation of glucose. Hypersecretion causes giantism or enlargement of boy areas. , hyposecretion causes pituitary dwarfs.
Thyroid Stimulating Hormone
Released by the anterior pituitary. A stimulating hormone, it stimulates normal development and activity of the thyroid gland.
Adrenocorticotropic Hormone Releasing Hormone
Released by the anterior pituitary. Stimulates adrenal cortex to release corticorsteroid hormones to help resist stressors
Gonadotropins
Released by the anterior pituitary. Follicle stimulating hormone, FSH, and luteinizing hormone, LH. THey regulate the function of the ovaries and the testes.
Prolactin
Released by the anterior pituitary. A protein hormone, it stimulates milk production.
Oxytocin
Stored in the posterior pituitary. A strong stimulant of uterine contractions and milk production.
Antidiuretic Hormine
Stored in the posterior pituitary. Chemical substance that inhibits and prevents urine formation. Can be inhibited by alcohol. Diabetes insipidus and diabetes mellitus can be caused by ADH mis production
Thyroid Gland
Locaed in the anterior throat. It’s composed of hollow follicles that produce the glycoprotein thyroglobulin.The thyroid gland is unique because it has the ability to store and slowly release its hormones as needed. Thyroid hormone affects every cell in the body except for the brain, spleen, and uterus.
Thyroid Hormone
Major metabolic hormone. Actually 2 hormones, thyroxine (T4) and triiodothyronine (T3). Thyroxine is the major hormone, but it’s all eventually converted into triiodothyronine.
Synthesis of Thyroid Hormone
- Thyroblobulin forms on the ribosomes of follicle cells and is discharged into the lumen and stored.
- Iodine from blood attaches to tyrosine, an AA, forming part of the thyroglobulin colloid.
- Thyroglobulin is taken back into the cell by endocytosis and combined with a lysosome before being released into the blood
Thyroid Gland Diseases
Graves Disease - hyperthyroidism
Myxedema - hypothyroidism
Cretinism- severe hypothyroidism
Thyrocalcitonin
Calcitonin. It’s most important role is to control calcium levels.
Parathyroid Glands
Embedded in the posterior of the thyroid gland. Usually 3-4 of them.
Parathyroid Hormone (PTH)
Most important hormone controlling the calcium balance in the blood. Triggered by falling calcium levels and inhibited by hypercalcemia. Increase levels by stimulating the skeleton, kidneys, or intestines by activating vitamin D.
Adrenal Glands
Found on top of the kidneys. Each has 2 funtional areas. The adrenal cortex, and the adrenal medulla.
Adrenal Cortex
Consists of 3 zones
- Glumerulosa
- Fasciculata
- Reticularis
Zone Glumerulosa
Produces mineral corticoids. Mainly aldosterone which balances water and minerals in the blood. Hypoaldosteronism is too little aldosterone. Aldosteronism is too much aldosterone.
Renin-Angiotensin System
The major regulator of aldosterone, kidney involvement of Na+ and K+ ion retention. Plasma concentration of Na+ and K+ influence the glomerulosa to increase K+ and decrease Na+. It’s controled by ACTH, and plasma concentration of the atrialnatriuretic factor, AF. inhibits aldosterone.
Zona Fasciculata
Secretes metabolic hormones, the glucocorticoids. They influence metabolism, help resist stressors, and are anti-inflammatory. Hormones include cotisol, cortisone, and corticosterone. Diseases include Addison’s disease, hyposecretion, and Cushing’s disease, hypersecretion.
Adrenal Medulla
Chromafin cells arranged in clusters. Has two main hormones, epinephrine and norepinephrine used when body is activated for fight-or-flight status. It increanses blood sugar, vessels constrict, heart beats faster, blood pressure increases.
Pancreas
Located partially behind the stomach. Has islets of Langerhan which produce hormones, and exocrine acinar cells.
Islets of Langerhans
Two types of cells.
- Alpha: Glucagon synthesizing, major target is the liver which reduces glucose into the blood
- Beta: Insulin producing, lowers blood sugar levels.
Diabetes Mellitus
Hyposecretion of insulin. Has 3 main signs: Polyuria, excessive urine output, polydipsia, excessive thirst, and polyphagia, excessive hunger.
Ovaries
Produce estrogen which is responsible for maturation of reproductive organs and sex characteristics. And progesterone which along with estrogen promotes breast development and menstrual cycles.
Testes
Produce mainly testosterone which initiates sex characteristics and reproductive organs.
Pineal Gland
Located in the third ventricle of the brain. Mainly secretes melatonin which increases at night and decreases during the day regulating the circadian rhythm.
Thymus
Located in the thorax, decreases in size with age. This is where T-cells mature. Produces thymopoietin and thymosine which are essential for immune response.
Age Effects
With age, function of all endocrine glands degrades, except for the parathyroid gland, which shows very little change with age.
