Principles of Endocrinology and the Endocrine Pancreas
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- Created by: amazingemilyjones
- Created on: 23-04-19 15:03
Principles of Endocrinology and the Endocrine Panc
Principles of Endocrinology and the Endocrine Pancreas
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Definitions
- Endocrinology: the study of the endocrine glands of the human body, the hormones they produce, their receptors, the intracellular signalling pathways involved and the diseases and conditions associated with the glands
- Hormone: chemical produced in ductless glands and secreted direcetly into the blood stream
- Endocrine: acts on cells or organs at a distant site
- Paracrine: acts on local cell or organ
- Autocrine: acts on cell which produced it
- Exocrine: chemical produced in glands with ducts and secreted to areas outside the blood stream
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Why do we need hormones?
- Organs in the body need to communicate with each other
- Nerve fibres: fast, local, short acting
- Hormones: slow, widespread, long term
- Interactions occur between these two systems leading to homeostasis
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Locations of the Main Endocrine Glands
What do hormones do?
- Control reproduction
- Oestrogen and testosterone are essential for reproduction and the perpetuation of mankind
- General growth, development and senescence
- Growth hormone is essential for growth to normal stature and average life expectancy
- Regulation of electrolyte composition of body fluids
- Vasopressin is essential for the control of body fluid volume
- Control energy metabolism
- Thyroid hormones are crucial to our ability to regulate our body temperature and thus survive on earth
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Control of Hormone Secretion
- Generally hormone levels are controlled by feedback mechanisms
- Sometimes cells making a hormone respond to levels of a particular chemical
- E.g. pancreatic beta-cells respond to glucose
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Negative Feedback
- Direct negative feedback
- An increase in the level of a circulating hormone directly decreases the secretory activity of the cells which make it
- Indirect negative feedback
- An increase in the level of a circulating hormone A decreases the secretory activity of cells responsible for secreting hormone B which stimulates the production fo hormone A
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Negative Feedback
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Positive Feedback
- An increase in the level of a circulating hormone increases its own production either directly or indirectly
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Endocrine Pancreas: Homeostatic Control of Metabol
- Glucose is the primary substrate for ATP production
- Glucose levels are controlled by two hormones secreted by endocrine cells of the pancreas
- insulin
- glucagon
- Regulation of glucose levels in the blood depends on the ratio of insulin to glucagon
- Short half lives, secreted on demand
- Act in antagonistic fashion to keep plasma glucose concentrations within the normal range (4-7.8mmol/l)
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Anatomy of the Pancreas
Glycogenesis
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Glycogenolysis
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Insulin
- Insulin secretion
- stored in granules in the cytoplasm of beta cells
- occurs in response to rising blood glucose detected by beta cells
- biphasic secretion into the blood - immediate release of stored insulin then subsequent release of stored and newly synthesised insulin
- incretin effect
- Insulin actions
- lowers blood glucose - helps glucose move into cells via glucose transporters
- stimulates biochemical activity in cells
- acts on insulin tyrosine kinase receptors
- Metabolism of insulin
- kidneys and liver (~50% each)
- half life ~5 minutes
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Carbohydrate Intake and Insulin Release
Insulin
- Most responsive tissues to insulin
- Skeletal muscle - myocytes
- Liver - hepatocytes
- Adipose tissue - adipocytes
- Insulin is an anabolic hormone
- Insulin promotes storage of glucose as:
- proteins (muscle)
- carbohydrates (liver)
- lipids (adipose tissue)
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Anabolic Actions of Insulin
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Anabolic Actions of Insulin
- Glucagon secretion
- stored in granules in cytoplasm of alpha cells
- occurs in response to falling blood glucose detected by alpha cells
- inhibited by insulin acting on alpha cells
- Glucagon actions
- raises blood glucose
- opposes actions of insulin
- catabolic hormone
- acts on glucagon G-protein-coupled receptors
- Metabolism of glucagon
- liver (~80%) and kidneys
- half-life ~5-6 minutes
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Catabolic Actions of Glucagon
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The Relationship Between Glucagon and Insulin
The Relationship Between Glucagon and Insulin
- Fed state
- body is absorbing nutrients, insulin dominates, net anabolism occurs
- ingested glucose used for energy production, excess is stored as glycogen or far
- amino acids go primarily to protein synthesis
- Fasted state
- regulation prevents low plasma glucose concentrations (hypoglycemia)
- glucagon predominates, the liver uses glycogen and non-glucose intermediates to synthesise glucose for release into the blood
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Diabetes Mellitus
- Main symptoms:
- hyperglycaemia (high blood glucose)
- glucosuria (glucose in the urine)
- polyuria (frequent urination especially at night)
- polydypsia (increased thirst)
- polyphagia (increased hunger)
- tiredness
- Treatments:
- type 1 - insulin
- type 2 - dietary/lifestyle management, drugs, insulin
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Diabetes Mellitus
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