Topic 7: Endocrine System Flashcards
System Overview
- Regulates growth, reproduction, metabolism (long-term events)
- Glands and tissues secrete hormones which travel in blood to target cells (= cell with specific receptors for the hormone)
- Blind to receptors + change cell activity
- Receptors (proteins) found:
1) On the cell membrane
2) Intracellular( Nuclear)
Water Soluble Hormones
- Peptides, proteins, catecholamines (= 1st messenger)
- Steps:
1) Hormone binds to cell membrane receptors (do not enter cell for their actions)
2) Hormone-receptor complex activates membrane proteins e.g. G-proteins
3) G-proteins then activate second messenger systems - e.g. cAMP, Ca2+
Example using cAMP (cyclic adenosine monophosphate) as 2nd messenger
1) Hormone binds to cell-surface receptor and activates G-protein(s)
2) G-protein activates adenylate cyclase (membrane protein)
3) Adenylate cyclase converts ATP to cAMP (=second messenger) - higher cAMP
4) cAMP activates protein kinases (in cytosol)
5) Protein kinase acts on other proteins (usually phosphorylates) to alter their activity - changes cell activity - e.g. Epinephrine on liver cells (activates cAMP) - causes breakdown of glycogen to glucose - released to blood
Why use 2nd Messenger Systems?
1) Hormone can’t enter cell (water soluble)
2) Rapid acting (enzymes already present - just activate)
3) 1 Hormone molecule –> many enzymes molecules activated – multiplies signal
4) Limited - messenger broken down or removed - e.g. cMAP broken down by phosphodiesterase in cell
Lipid Soluble Hormones
- Steroids (cortisol) and thyroid hormones
- Trigger protein synthesis - takes time - slow but long lasting response
Steps of Action for Lipid Soluble Hormones
1) Enter target cell and bind to intracellular (nuclear) receptors in cytosol or nucleus
2) Hormone- receptor complex binds to a specific region on DNA (Activates genes) - starts gene transcription
- Produces messenger RNA (mRNA)
3) mRNA attaches to ribosomes to produce proteins (translation)
Regulation of Hormone Secretion into Blood
- Stimuli acting on an endocrine gland may be:
1) Humoral Stimulus
2) Neural Stimulus
3) Hormonal Stimulus
Humoral Stimulus
- Stimulus = ions/nutrients
Humoral Stimulus Example #1
- Higher blood glucose (after eating carbs)
- Pancreatic B cells (islets of langerhans) detect glucose and release insulin – lower blood glucose (-ve feedback)
Humoral Stimulus Example #2
- Lower blood Ca2+
- Parathyroid glad detects low Ca2+ releases parathyroid hormone (PTH) – higher resorption (breakdown) by
1) Higher osteoclast activity
2) lower Osteoblast activity - Higher blood Ca2+ (-ve feedback)
Neural Stimulus Example #1 and #2
Heart rate (HR) Resting HR --- "surprise"--> SNS - Preganglionic directly to --nt = ACh--> Adrenal Medulla -- Epinephrine + NE--> Higher HR + force of contraction
Note: Moving out of homeostasis in a controlled manner (Neither + or -)
Uterine Contraction –> hypothal –> post pituitary –> Oxytocin
(+ve feedback)
Hormonal Stimulus
e.g. Metabolism
Low metabolism –> Hypothalamus: Thyrotropin releasing hormone (TRH) –> Ant. pituitary thyroid stimulating hormone (TSH) –> Thyroid Gland: thyroxine (T4) –> T4 or T3 (in target tissue or liver) –> higher metabolism (overall -ve feedback)
Stress
- Any external or internal stimulus e.g. surgery, infections, strong emotions, exams
- Triggers a set of body changes called the General Adaptation Syndrome
- All co-ordinated directly or indirectly by the hypothalamus
Stress Phases
1) Alarm Reaction (Fight or Flight Response)
2) Resistance Reaction
3) Exhaustion
Phase 1: Alarm Reaction
- DIAGRAM
- Immediate = NS
- Effects of NS and hormones:
1) higher blood glucose (energy) - SNS inhibits insulin release - Epi, NE trigger conversion of glycogen to glucose in the liver
2) Higher HR, force of contraction
3) Lower blood flow to skin, abdominal viscera - more available to skeleton. and cardiac muscle + brain (O2 + glucose to working organs)
4) Lower digestion, urine production
