Chapter 20 Notes
Chapter 20 Notes 80887 - BIOL 3150 - 001
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This 14 page Class Notes was uploaded by Abigail Towe on Monday November 9, 2015. The Class Notes belongs to 80887 - BIOL 3150 - 001 at Clemson University taught by Tamara L. McNutt-Scott in Fall 2015. Since its upload, it has received 20 views. For similar materials see Functional Human Anatomy in Biological Sciences at Clemson University.
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The Endocrine System: ● a system of ductless glands that work together along with the Nervous System to coordinate and integrate the activities of the body’s cells. Thus, regulating body functions. Endocrine System Nervous System Communication Hormones Neurotransmitters Method: targets: Cells with receptors specific response time & effect slow. metabolic rapid. activities contraction/secretion range of effect widespread; general localized; specific response duration long-lasting short term recovery time slow rapid; immediate Endocrine = ductless glands ● the cells release the product into interstitial fluid (blood or lymph) ● chemical messengers= hormones Endocrine system organs: ● Organs are small and not as valued as other organs ○ example: pituitary- size of pinky but it has a large impact on body ○ Other endocrine organs: ■ Pituitary (anterior and posterior) ■ pineal gland ■ thyroid ■ parathyroid gland ■ adrenal gland Endocrine system- does not display anatomical continuity- organs are scattered throughout the body Target organs - ● comprised of target cells ● has receptors that hormone binds to and affects ○ can cause wide variety of responses: ■ mobilization, maintaining water levels, growth and development, regulation of cellular metabolism and energy balance Endocrinology- study of ductless glands, the hormonal products, and how they affect target organs Hormones are classified based on their chemical structure: Hormone Type Chemical Structure peptide hormones: chains of amino acids hormones that have amino acid biogenic amines derivatives steroid hormones derived from lipids fatty acid-derived hormones eicosanoids eicosanoids - are signaling molecules made by oxidation of 20-carbon fatty acids. Hormone Regulation through Feedback Loops 1. Negative Feedback loop: a. most common b. there is an OPPOSITE directional change. c. the system causes a decrease/end to original stimulus d. example: Human body temperature i. The hypothalamus of a human responds to temperature fluctuations and responds accordingly. ii. If the temperature drops, the body shivers to bring up the temperature iii. If it is too warm, the body will sweat to cool down due to evaporation. 1. Stimulus = eating food causes a rise in blood glucose levels 2. The insulin-secreting cells of pancreas detect high blood glucose levels. 3. Pancreas secretes hormone: insulin 4. insulin causes liver cells to take up glucose and store it as glycogen 5. as body cells and liver take up blood glucose, glucose levels decrease and the insulin being released stops 6. body is now returned to homeostatic blood glucose level 2. Positive Feedback loop: a. same directional change b. the system causes an increase or exaggerated response over the original signal. c. output is increased d. usually the control is episodic or infrequent - meaning they do not require continuous adjustments e. An example of a positive feedback mechanism is blood clotting. i. Once a vessel is damaged, platelets start to cling to the injured site and release chemicals that attract more platelets. ii. The platelets continue to pile up and release chemicals until a clot is formed. Summary: Positive feedback mechanisms enhance the original stimulus and negative feedback mechanisms inhibit it. Hypothalamic Control of Endocrine System: ● “master control” of endocrine system because it oversees most activities, but NOT ALL endocrine glands/structure are controlled by hypothalamus. ● However, the activity that is controlled is done via the pituitary gland ● Hypothalamus is responsible for: 1. producing regulatory hormones stimulate or inhibit anterior pituitary hormone secretion. 2. produces hormones that are stored and released from posterior pituitary a. hormones = antidiuretic + oxytocin 3. stimulates hormone secretion of adrenal medulla via sympathetic innervation a. hypothalamus is overseer of autonomic nervous system Pituitary Gland (Hypophysis) ● located below the hypothalamus ● structurally and functionally divided: ○ anterior pituitary “adenohypophysis” ○ posterior pituitaryneurohypophysis” ● this gland is derived from embryonic structures Hormones secreted from the anterior pituitary Hormone: tropic? Secreted by: Acts on: Thyroid-stimulating thyrotropic cells thyroid gland to hormone (TSH) release thyroid ✓ hormone prolactin (PRL) mammotropic cells mammary glands to stimulate milk production adrenocorticotropic ✓ corticotropic cells adrenal cortex to hormone (ACTH) cause release of corticosteroids growth hormone (GH) ✓ somatotropic cells all body tissues to grow (esp. bone, muscle, adipose CT) follicle-stimulating gonadotropic cells gonads ✓ hormone (FSH) & (testes/ovaries) luteinizing hormone to stimulate (LH) development of gametes (sperm/oocyte) melanocyte-stimulating pars intermedia cells melanocytes in hormone (MSH) (in anterior pituitary) epidermis to stimulate melanin synthesis Tropic hormones are hormones that have other endocrine glands as their target. Most tropic hormones are produced and secreted by the anterior pituitary. Control of Anterior Pituitary Secretions: → Hypothalamo-Hypophyseal Portal System ● is a system of blood vessels in the brain that connects the hypothalamus with the anterior pituitary. ● function = transport and exchange of hormones to allow a fast communication between both glands. ● The fenestrated structure of capillaries in the hypophyseal portal system facilitates a rapid exchange between the hypothalamus and the pituitary, with only a small amount of hormones needed to stimulate an accurate effect in the respective target organs in the body. ● Fenestrated capillaries have pores in the endothelial cells that are spanned by a diaphragm of radially oriented fibrils and allow small molecules and limited amounts of protein to diffuse. Posterior Pituitary: ● aka Neurohypophysis ● does NOT produce any hormones! ● made up of Pituicytes (main cell type of posterior pituitary gland) ● has hypothalamo hypophyseal tract ○ a tract of nerves connecting the hypothalamus and the posterior pituitary Adenohypophysis= anterior pituitary gland neurohypophysis= posterior pituitary gland Thyroid Gland ● located: in neck ○ inferior to larynx ○ anterior to trachea ● surrounded by capsule made from connective tissue ● has two lobes (left and right) ● isthmus connects the left and right lobe ● composed of follicle cells (simple cuboidal epithelium) ○ follicle cells surrounded by central lumen ○ filled with viscous fluid that is rich in protein = colloid ○ follicle cells produce thyroid hormones ○ colloid stores the thyroid hormones ■ note: this is the only hormone that is made “in advance” and store extracellularly ● parafollicular cells: produce calcitonin ○ located in clusters between follicle cells or individually ● Negative Feedback inhibition of releasing thyroid hormone: 1. stimulus (low body temperature) 2. hypothalamus then secretes thyrotropin-releasing hormone (TRH) → anterior pituitary 3. the thyrotropic cells in anterior pituitary then release thyroid- stimulating hormone (TSH) 4. TSH stimulates follicular cells of thyroid gland to release thyroid hormone (TH) 5. TH stimulates target cells to increase metabolic activities → to increase basal body temperature 6. hypothalamus detects increased temperature → inhibits secretion of TRH a. so TH blocks the interactions of TRH from hypothalamus to anterior pituitary so that formation of TSH is prevented. Parathyroid gland: ● located: on the posterior surface of thyroid - wraps around the backside ● function: produces parathyroid hormone (PTH) ● Operates by: 1. parathyroid gland detects low blood calcium levels → secrets PTH in bloodstream 2. target organs respond to PTH → causes increase of blood calcium levels a. this is done by osteoclasts releasing calcium because they resorb bone connective tissue b. also: intestine increases absorption of calcium (with help from calcitriol) 3. rising calcium levels in blood prevents release of PTH into bloodstream ● calcitriol promotes calcium absorption Parathyroid ^ Thyroid^ Adrenal Glands: ● pyramid shaped ● paired ● superior to each kidney ● retroperitoneal- behind the peritoneal ● no ligaments to attach them - so they are held in place by fat and strategically placed fascia to minimize movement ● it is very well vascularized - (common features with endocrine organs) ● two regions: cortex and medulla (structurally different - like how the anterior and posterior pituitary are different) ○ cortex- outer region ■ has 3 layers ● zone glomerulosa- balls of cell ● zone fasciculata - stacks of cells ● zone reticularis- cluster of cells ■ and produces corticosteroids ● which are important for life - regulate nutrients, water, sodium ● we need to know: do you know where GH is from? and what it’s basic function is? ○ medulla- inner region ■ looks more like nervous tissue ■ chromaffin cells- modified postganglionic cells of somatic NS (so modified neurons) ■ releases biogenic amines into blood circulation and has fairly good halflife ■ produce epinephrine and norepinephrine ● they have longevity, and different functionality. ● epinephrine & norepinephrine- are hormones that are secreted by populations of chromaffin cells (when stimulated by the sympathetic division of the autonomic nervous system) ○ because hormones are released more slowly than nerve impulses and their effects are longer lasting, the secretion of these hormones help prolong the effects of the sympathetic stimulation. so the sympathetic responses continue to linger because these hormones are still present in the bloodstream to still affect their target cells. ○ they are structurally and functionally different because of where these parts arose from during embryonic development Histology slide : book explains this Table 20.6 ● usually you see cortex- medulla- cortex in slides ● Zone Glomerulosa- balls of cells ○ produces: mineralocorticoids ■ the main mineralocorticoid is aldosterone- regulates sodium ● so it also regulates water ● Zone Fasciculata ○ produces glucocorticoids ■ main glucocorticoid is cortisol - regulates glucose in blood ■ and plays a role in lipid and protein metabolism ● Zone Reticularis: clusters of cells ○ produces gonadocorticoids ■ minor role in adults ■ the time they really have a big influence is in puberty - important they make a transition at the time of puberty ■ can be androgens and estrogens ^^ these are all types of corticosteroids= hormones important for survival of the organism ● important because they regulate important things: water, sodium , nutrients, reproduction Pancreas ● heterocrine organ - but majority of function is exocrine , like 1% of mass is endocrine function ● endocrine function in pancreatic islet: ○ main endocrine cells found here: ■ alpha cells- glucagon ● works to regulate blood glucose levels (increases levels of blood glucose) ■ beta cells- insulin ● works antagonistically with glucagon to regulate blood glucose levels (decreases blood glucose levels) ■ delta cells - somatostatin ● somatostatin from islets helps to regulate the alpha and beta cells - so it indirectly regulates the blood glucose levels ■ F cells - pancreatic peptide ● this is an interesting hormone that acts locally - it helps to digest the digestive processes occurring in the GI tract ○ with all these hormones we are growing, regulating, and digesting ■ basically directing nutrient processes Pineal Gland ● located in part of the diencephalon - near the epithalamus ● composed of: pinealocytes ● also called “brain sand” - small grains of calcareous material . a sign of aging. ○ older people have more sand ○ you can use pineal gland to map where you are in the brain because the sand is easily seen ● produces melatonin -hormone that is cue for night ○ cyclic release ■ increases at night, decreases during the day ○ cue for night ■ produces melatonin when no or little light. when light is present - it’s shut down Thymus ● makes hormones but they don’t travel outside the thymus ● what: fatty structure ● located: superior to heart, posterior to sternum, within the mediastinum ● it’s a bilobed structure ● large in infants, but regresses with age (puberty is marker here) ○ this transition is noted by functional tissue of thymus replaced with fat and fibrous CT so it become inactive in function ● function: regulate and modulate body immunity ○ lymphatic system ● has thymopoietin and thymosin stimulate and promote differentiation, growth, and maturation of lymphocytes (T cells) ○ lymphocytes arrive in bone marrow, and then go to thymus to get “educated” into T cells ○ so this is why diseases like AIDS are bad- it causes you to lose T cells. ■ so once you lose T cells, you can’t get them back. Gonads ● produce steroidal sex hormones ● controlled by gonadotropins (FSH & LH) ○ ovaries ■ hormones produced by ovaries: estrogens and progestins ● select cells of ovarian follicle produce these in the ovaries ○ testes ■ produces: androgens- ● produced by Leydig cells (interstitial cells) of testes ○ testosterone is most prominent of androgens ■ produces inhibin produced by Sertoli cell (sustentacular cells) ● inhibit GnRH release by hypothalamus - gonadotropin releasing hormones (GnRH) Non-Endocrine Organs - have endocrine functions ● heart- ○ produces atrial natriuretic factor (ANF) “atriopeptin” ○ produced by atrial muscle cells & released in response to elevation in blood pressure ● Gastrointestinal tract ○ Variety of hormones released from enteroendocrine cells, which are found throughout GI tract ■ primary function to regulate digestive processes ● kidney- ○ produces two hormones: ■ Erythropoietin - signal bone marrow to increase red blood cell production ■ Renin- initiate the Renin-Angiotensin system & stimulates thirst and elevation of bp ● renin is an enzyme! ● renin does not actually do this, it just starts the cascading of events ● skin ○ cholecalciferol ■ this is the precursor molecule that allows skin to produce vitamin D from sunlight by changing the structure ■ released into circulation and activated in kidney (calcitriol) ● adipose tissue ○ leptin- peptide hormone ■ appetite control / the feeling of “fullness” ■ so pumping people with these hormones alone doesn’t make them feel full - more complicated than that ○ resistin- peptide hormone ■ linked to high levels of ▯bad▯ cholesterol → which increases risk of heart disease Endocrinopathies- any disease resulting from a disorder of an endocrine gland or glands ● caused by: ○ too much hormone (hypersecretion) ○ too little hormone (hyposecretion) ○ receptor isn’t working (receptor dysfunction so they won’t respond)