Feb 11th Flashcards
Claude Bernard
- father of modern physiology
- our internal environment remains remarkably constant despite changes in the external milieu
Walter Cannon
- coined the term “homeostasis” to describe the relative stability of the internal environment
Homeostasis
- SENSOR: detects shift in physiological variable outside normal range
- INTEGRATION/CONTROL CENTER: Processes the information and determines the appropriate response
- EFFECTOR: Carries out the response to restore balance
Homeostasis - negative feedback loops
Negative feedback loops reverse a change to maintain balance, unlike positive feedback loops, which amplify a response.
Ex: Body Temperature Regulation
- If too hot: The body sweats to cool down.
- If too cold: The body shivers to generate heat.
what does homeostatic control rely on?
- Sensor: constantly monitors
- Integrating center: coordinates
- Response system: changes
components of homeostatic systems
- Sensory system (monitor)
- Integrating center
- Response system (adjustment)
- Negative feedback
Major regulatory systems
- skin
- cardiovascular
- renal
- digestive
- respiratory
- musculo-skeletal
the regulated factors
- water
- electrolytes/ pH
- nitrogenous compounds
- oxygen
- carbon dioxide
- temperature
- toxicants
hyper function
too much hormone
hypo function
too little hormone
resistance
too little effect
what is the endocrine gland
a tissue which releases (secretes) a substance into the blood stream; this substance then travels via the blood to influence a target cell
what makes a chemical a hormone
a chemical messenger secreted by glands, travelling through the bloodstream to regulate physiological functions
types of hormones
- proteins & polypeptides (<100 AA)
- steroids (cholesterol derivatives)
- glycoproteins
- amines (catecholamines or thyroid hormones)
classic minkowski experiment (1889)
discovery of insulin
- pancreas removal in dogs (diabetes symptoms appear)
- pancreatic tissue implantation (symptoms prevented)
Banting & Best (1921)
further discovery of insulin
- found antidiabetic substance in pancreatic extracts
- injecting extracts - prevents elevated blood glucose (diabetes symptoms)
what is the type, function and forms of insulin
type: peptide hormone from beta cells of the pancreas
function: helps glucose absorption in muscle and fat tissue
forms: inactive - hexamer
active - monomer
Autocrine Signaling - hormones
A cell secretes a hormone or chemical messenger that binds to receptors on the same cell that released it.
Paracrine Signaling - hormones
A hormone or chemical messenger is released by one cell and affects nearby cells without entering the bloodstream.
Endocrine Signaling - hormones
A hormone is released into the bloodstream, traveling to distant target organs or tissues.
What do hormones bind to?
Hormones bind to specific receptors in target cells to trigger a response.
How specific are hormone receptors?
Very specific to their hormone, but non-specific binding (overspill) can occur.
Why is receptor-hormone turnover important?
Continuous formation & breakdown of receptor-hormone complexes is essential for proper signaling.
Where are most hormone receptors found?
On the plasma membrane of target cells (for peptides & protein hormones).
Where do steroid & thyroid hormones bind?
Inside the target cell, to intracellular receptors.
What do transmembrane receptors do?
They bind hormones outside the cell and trigger intracellular signaling.
How do transmembrane receptors activate signals?
By triggering cytoplasmic pathways, often involving phosphorylation & enzyme activation.
What are the two main effects of transmembrane receptor signaling?
- DNA → mRNA → Protein response (gene expression changes).
- Local effects (e.g., enzyme activation in the target cell).
Adenylate cyclase pathway
- Hormone + receptor, G-
proteins dissociate - α-subunit activates AC
- Catalyzes product of
cAMP - Removes regulatory unit
from PK - PK activates other
molecules (hormonal
response)
Epinephrine & adenylate cyclase
- Epinephrine binds to β–adrenergic
receptor on liver cell - G-proteins activated – subunit
carrying GDP dissociates, GDP →GTP - Subunit activates adenylyl cyclase
which catalyzes ATP → cAMP - cAMP activates PKA, which activates
phosphorylase - Phosphorylase converts glycogen to
glucose-6-phosphate - Glucose-6-phosphate → glucose
(released from liver)
Phospholipase C-Ca2+ pathways
- Hormone + receptor, G-
proteins dissociate - Activates PLC
- Causes breakdown of
membrane phospholipid to
IP3 - IP3 binds to endoplasmic
reticulum - Release of stored Ca2+ into
cytoplasm - Ca2+ activates other
molecules (hormonal
response)
what do alpha-adrenergic receptors activate
phospholipase C
what do beta-adrenergic receptors activate
adenylate cyclase
Steroid hormone receptors
- Steroid hormone (e.g. estrogen,
androgen) transported bound
to plasma carrier protein
* Lipophilic i.e. they move across
plasma membrane - Steroid hormone binds cell
cytoplasm receptor - Translocates to the nucleus,
binds to DNA
* Acts as a transcription factor - Stimulates gene transcription
- Protein products
- Response
Thyroid receptors
- Thyroxine (T4) + carrier binding protein
- T4 → T3 (triiodothyronine)
- T3 uses binding proteins to enter nucleus
- Hormone-receptor complex binds DNA
- New mRNA
- Protein
- Response
What did Lefkowitz & Kobilka study?
G protein-coupled receptors (GPCRs) and how cells sense their environment.
Why are GPCRs important?
They play a key role in cell signaling and are targets for nearly half of all drugs.
