3-5 Flashcards by Anna Hill

Define Homeostasis

The maintenance of relatively constant conditions in the body by physiological processes that act to counter any departure from the normal

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Who first used the term homeostasis

Walter Bradford Cannon

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Which variables are controlled in mammals

1) core body temperature
2) Osmotic Pressure
3) Arterial blood pressure 4) extracellular fluid volume
5) Blood gas concentrations
6) Concentrations of extracellular solutes like Na+, K+, and protons

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What is a conformer

An organism who do not complete active homeostasis as they have the same components as surroundings
- Hag fish

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Regulators?

GRAPH

Homeostatic organims

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Poikilothermy

An organism that does not regulate it’s own internal temperature—> Naked Mole rat

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How is homeostasis usually maintained

Negative feedback loops

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Positive feedback examples

x 3

Urination
Parturition
Metamorphosis

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How does negative feedback work

Disturbance affects controlled system
Sensor picks up difference
Inverting amplifier
Response which affects the controlled system

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What are the main sensors for negative feedback loops in mammals
x 5

Thermoreceptors (skin and hypothalamus)
Osmoreceptors (hypothalamus)
High pressure baroreceptors (carotid sinus, aortic arch and afferent arteriole of kidney)
Low pressure baroreceptors (atria, great veins and pulmonary vasculature)
Chemoreceptors (medulla oblongata and carotid and aortic bodies)

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What are neurocrine transmitters

Substances released by neurones in the immediate vicinity of target cells or into the blood—>neurotransmitters are a subset of this group

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Endocrine transmitters

Hormones

1) Synthesised by a specific tissue
2) Secreted into the bloodstream
3) Change the activity of that target tissue or organ

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Paracrine transmitters

‘local hormones’
Diffuse through extracellular fluid to reach and affect target cells of a different cell type to itself
Histamine and Nitric oxide

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Autocrine transmitters

Like paracrine but act on same cell type as those that secrete them

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Cytokines

Transmitters released by immune cells

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Pheromones

Released by animal into environment to affect physiology or behaviour of another animal of the same species

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Water-soluble hormones

explain and 3 types

Stored in vesicles and released by exocytosis—>travel loose in blood and bind to membrane-based receptors

TYPES

1) Peptide/ protein hormones
2) Glycoproteins
3) Catecholamines (derived from tyrosine)

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Lipid-soluble hormones

what and 4 types

Diffuse out of cells once made and transported in blood bound to special carrier proteins. Usually intracellular receptors

1) Steroid hormones
2) Thyroid hormones
3) fatty acid derivatives
4) Indolamines (melatonin)

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G-protein coupled receptor

GRAPH

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How to deactivate g-protein coupled receptor

Upon hydrolysis of GTP to GHDP on α-subunit will cause it to rebind to βγ-subunit and become inactive
- in cell a phosphodiesterase hydrolyses cAMP and terminates cell response

Lipid-soluble hormone receptors

Usually in cells and act directly as transcription factors

Getting rid of chemical messengers and half-lives

Most hormones metabolised by liver or kidneys

Half-lives of hormones in plasma can vary from 1-3 minutes for adrenaline to 7 days for thyroxine (T4)

Blood-brain barrier

Prevents circulating substances which also act as neurotransmitters from acting on the brain

its formed of endothelial cells being connected by particularly tight junctions
held there by glial cells foot processes

Where is the blood-brain barrier ‘leaky’

Posterior pituitary gland
Median eminence
Pineal gland
Circumventricular organs

fenestrated BBB so release hormones into blood or detect their presence

Where is the hypothalamus

Small region of the forebrain above the pituitary gland

What does the hypothalamus do?

Received input from many sources relating to both internal and external environment —integrates information and controls physiological response—>homeostatic control centre

The hypothalamus contains multiple intercommunicating nuclei

These are collections of nerve bodies

Leptin example | intro

Protein hormone secreted by white fat cells and detected in arcuate nucleus of hypothalamus. Use levels to establish body’s nutritional state

What if leptin levels are high?—so well fed

1) Feeding behaviour suppressed 2) Release for TRH 3) activates hypothalamic-pituitary-thyroid axis—>increase metabolic rate 4) other function regulated reproductive axis in women

Posterior pituitary

Downgrowth of the brain made of bundles of axons of nerve cells whose bodies are in the hypothalamus

Anterior pituitary

Originates from Rathke’s pouch and lies outside of the BBB—>produces hormones

ADH

Released from PP - release at high osmotic pressure and in lower concentrations when there is low blood volume 1) Acts on kidney collecting ducts to increase water permeability 2) at higher concentrations causes vasoconstriction and compensates for loss of blood volume

Oxytocin

released by PP mainly in reproductive functions like the fergusson reflex (where stretch of cervix then causes more contractions to push baby out, expanding cervix more)

What is a portal vein

A vein that travels between two capillary beds

Anterior pituitary hormones

Involved mostly in control of endocrine glands elsewhere in the body 1) Glycoproteins 2) Somatomammotropins 3) Pro-opiomelanocortin

Hypothalamic-pituitary-thyroid axis

Hypothalamus send hormones to AP which cause release of another hormone which causes an endocrine gland (like thyroid) to release another hormone —one of the jobs of this hormone is to inhibit the releasing hormone from hypothalamus=LONG-LOOP FEEDBACK Short is from AP hormone inhibit hypothalamus and ultrashort is hypo prevents hypo

TPT example

GRAPH

Pulsatility

The releasing of hormones in bursts to prevent receptor down-regulation

Feed-forward control

A mechanim by which to prevent ‘overshooting’ the set point and requiring negative feedback to go the other way - like in drinking Prevents oscillating levels

What is dynamic equilibrium

Where there is no net force acting across a membrane as the concentration gradient is equal to the electrical gradient. Represented by E (subscript of the ion)

Why do we say that concentration stays roughly constant

very few ions move across membrane before dynamic equilibrium

What is the Nernst equation? | at 20 degrees

E (ion) in mV = (58/z) log10(conc ion out/conc ion in)

what does it mean if the membrane potential does not equal the equilibrium potential of one ion

Then the membrane is permeable to more than one ion

Line predicted by the GHK equation fits the resting membrane potential of frog muscle cells than the line predicted by nernst K What is the GHK equation

Picture

What does P represent in the GHK equation? | goldman-Hodgkin-katz

The relative permeability of the ion

What is ouabain

- toxin - binds to sodium pump - stops from working - small loss of -5mV at first - then slow to zero

What is the actual name of the sodium pump | - what does it do

Sodium-potassium ATPase - pumps out 3Na+ with 2K+ into the cell - requires ATP

role of sodium pump

Maintain the concentration gradients of sodium and potassium over long term and the slow leaking increases the concentration of sodium in the cell

How to change membrane permeabilities to ions

Open more channels specific to that ion