endocrine system

direct cell communication

cells communicate by physically interacting with one another

direct cell communication features

gap junctions are specialised channels connecting adjacent cytosol allowing direct transfer of ions and small molecules
cell surface marker interaction is where one cell has a specific marker and another has the complimentary molecule that fits in
receptor regulation either upregulation increasing sensitivity or down regulation decreasing sensitivity

indirect cell communication

cells communicate by chemical messengers

indirect cell communication features

a secretory cell releases a messenger into the extracellular fluid, the messenger binds to the receptor on the target cell and receptor binding triggers a specific response in the target cell

types of chemical messengers

autocrine, paracrine, endocrine/hormone, cytokines, neurotransmitters and neurohormones

types of chemical messengers - autocrine, paracrine and endocrine

autocrine: bind to receptors and exert their effects on the same cell that secretes them like growth factors in cell proliferation
paracrine: secreted by one cell and diffuse to nearby target cells like histamine from damaged cells acting on nociceptors
endocrine: secreted by endocrine glands into the blood like insulin for blood glucose regulation

types of chemical messengers - cytokine, neurotransmitter and neurohormone

cytokine: secreted by small protein immune cells like interleukins and interferons
neurotransmitter: released form axon terminals of neurons to signal across the synapse like serotonin and glutamate
neurohormone: secreted by neurosecretory cells of the nervous system rather than the endocrine system like ADH and oxytocin

endocrine system

controls and regulates functions of multiple body systems maintaining long term regulation via hormonal regulation eg. controlling labour and regulating blood glucose

endocrine glands

secrete hormones into interstitial fluid and the blood stream with endocrine glands primary function is hormone secretion like pituitary, thyroid, pineal, adrenal and parathyroid while endocrine tissues secondary function is hormone secretion like hypothalamus, thymus, pancreas, ovaries and testes

exocrine glands

do not produce hormone but secrete products into ducts that leads to body cavities or surfaces like sweat glands, mucous glands or sebaceous glands

types of hormones

peptide and steroid hormones

types of hormones - peptide

chains of amino acids which are water soluble, travel freely in the blood with no carrier proteins, bind to membrane receptors, activate secondary messengers and cause short term fast effects like insulin and ADH

types of hormones - steroid

derived from cholesterol which are lipid soluble, travel bound to carrier proteins in the blood, diffuse across the cell membrane, bind to intracellular receptors and alter gene expression casing long term slow effects like estrogen and testosterone

mechanisms of hormone action

must bind to specific receptors on the cell membrane, in the cytosol or in the nucleus, receptor binding triggers cellular responses and hormone levels are regulated by negative feedback

hormone concentration factors

rate of production, rate of delivery and rate of degradation/elimination

pancreas - anatomy

located retroperitoneally extending in an oblique and transverse position

pancreas - function

primary/exocrine function is to produce digestive enzymes and secondary/endocrine function is to produce hormones for blood glucose regulation

pancreas - pancreatic acinar cells

exocrine functions to secrete digestive enzymes aiding the break down of carbohydrates, proteins and fats

pancreas - islet of langerhans

beta cells secrete insulin which decreases blood glucose levels
alpha cells secrete glucagon which increases blood glucose levels
delta cells secrete somatostatin which inhibits glucagon and insulin as well as GH, IGF1, TSH, gastrin, prolactin and secretin
epsilon cells secrete ghrelin which increases appetite while, leptin secreted by adipose tissue decreases appetite

insulin - functions

increases cellular uptake of glucose and amino acids in the liver, muscles and adipose tissue
liver increases glycogen formation and decreases glucose production
muscles stimulates glycogenesis
adipose tissue stimulates lipogenesis
enhances glucose transport activity
regulates intermediary metabolism

insulin - post traditional modification

insulin mRNA is translated as a single chain precursor called pre-proinsulin which is inactive form
signal peptide is removed and the disulfide bond forms producing proinsulin
c peptide is cleaved off generating the mature and active form of insulin

insulin - regulation

stimulated by increased blood glucose, increased amino/keto acids and parasympathetic neural input like rest and digest
inhibited by sympathetic stress induced responses like fight and flight

insulin - process

eating food increases blood glucose levels
pancreatic beta cells detect this and secrete insulin
insulin enters the blood stream causing the body to take up glucose
blood glucose levels decrease

glucose transporters

membrane proteins that transport glucose across the cell membrane

types of glucose transporters

GLUT1, GLUT2, GLUT3 AND GLUT4

types of glucose transporters - GLUT4

only insulin dependent transporter which is stored inside cells in vesicles when insulin is low, when insulin is present it stimulates these vesicles to move to the cell membrane, allowing ells to take in glucose after meals

glucagon

liver stimulates gluconeogenesis and glycogenolysis
adipose tissue stimulates lipolysis

glucagon - regulation

hypoglycaemia
low blood glucose as less glucose is up took into alpha cells by GLUT1
intracellular glucose levels drop
ATP production decreases
ATP sensitive potassium channels close
potassium cells accumulate inside the cell causing it to depolarise
voltage gated calcium channels opne
calcium enters the cell casing intracellular calcium levels to increase
calcium triggers glucagon release via exocytosis

GLP1 and ozempic

GLP1 is a gut hormone released after eating enhancing insulin secretion in a glucose dependent manner but Ozempic is a drug binding to GLP1 receptors mimicing the effects used for weight management and diabetes

diabetes and Alzheimer

brain becomes less sensitive to insulin when someone has alzhimers’s making it harder for brain cells to use glucose properly causing reduced energy for neurons leading to cognitive decline and neurodegeneration

type I diabetes

insulin dependent diabetes mellitus, immune system destroys beta cells in the pancreas therefore, no insulin can be produced leading to hyperglycaemia

type II diabetes

progressive condition where the body becomes resistance to insulin caused by poor diet, inactivity, overweight, genetics and family history and can be shown by polyuria, polydipsia and polyphagia

diabaetes current treatment

type I: insulin injections/pumps, continuous glucose monitor and automated insulin delivery system
type II: healthy eating, physical activity, weight management and medications like metformin

diabetes current research

beta cell transplant: improves glycaemic control and reduces insulin dependence but there is a shortage of donor islets and requires life long immunosuppressive therapy
steam cell transplant: renewable source of insulin producing cells but is a complex procedure and immune rejection is possible