6. Endocrine System 2 Flashcards
1
Q
Describe the modes of transmission of hormones
A
- Endocrine: Hormones are released by glands or specialized cells into the bloodstream to influence the function of cells in another part of the body.
- Neurocrine: Hormones are secreted by neurons into the circulatory system to influence the function of cells in another part of the body.
- Autocrine: Hormones are secreted by cells into the extracellular fluid and affect the function of the same cells that produced them.
- Paracrine: Hormones are secreted into the extracellular fluid and affect the function of neighboring cells of a different type.
- Exocrine: Hormones are secreted to the exterior of the body (e.g., the lumen of the small intestine) and affect cell activity distal to the point of excretion.
2
Q
Where are the receptors for protein hormones located? steroid hormones? thyroid hormones?
A
- in or on the cell membrane surface.
- cell cytoplasm
- cell nucleus
3
Q
Describe down and up regulation of cell receptors
A
- Downregulation: Increased rate of receptor degradation induced by an excess of the hormone. A safety mechanism to prevent chronic overstimulation.
- Upregulation: Increased number of receptors, often due to a deficiency in the hormone.
4
Q
What are the two types of receptors located on the cell membrane?
A
- G-protein linked hormones receptors
- Enzyme-linked hormone receptors
5
Q
Describe G-protein linked hormones receptors
A
- seven transmembrane segments that loop in and out of the cell
- parts of the receptor that protrude into the cell membrane are coupled to G proteins
- three parts - a, b and g
- Gi - inhibitory; Gs - stimulatory - when the hormone binds to the receptor it activates the G protein causing
- opening or closing of cell membrane ion channels or
- change in the activity of an enzyme in the cytoplasm
Hormone
6
Q
Describe Enzyme-linked hormone receptors
A
- when activated function directly as enzymes or are closely associated with enzymes that they activate
- pass through the membrane only once
- hormone binding site is on the outside of the cell
and the catalytic or enzyme binding site is on the
inside - when the hormone binds to the receptor
- activates (or inactivates) enzyme immediately inside the
cell membrane
7
Q
Describe what is meant by a second messenger system
A
- Hormones activates a single type of membrane receptor
- the second messenger does the rest
- Second messengers allow amplification of hormone signals by activating multiple downstream molecules for a larger response.
8
Q
Describe adenylyl cyclase- cAMP
A
- A type of secondary messenger system
- binding of the hormone to receptor stimulates the adenylyl cyclase (a membrane bound enzyme)
- adenylyl cyclase catalyzes the conversion of a small amount of cytoplasmic ATP into cAMP
- cAMP activates cAMP-dependent protein kinase
- which phosphorylates specific proteins in the cell triggering biochemical reactions - cAMP = activates a cascade of enzymes
9
Q
Describe phospholipase C
A
- hormones activate transmembrane receptors that
activate the enzyme phospholipase C - phospholipase C catalyzes breakdown of some phospholipids in the cell membrane
- PIP (phosphatidylinositol biphosphate) broken down
into two separate second messengers; IP (inositol
triphosphate) and DAG (diacylglycerol) - IP mobilizes calcium ions from mitochondria and
endoplasmic reticulum - calcium then has its own second messenger effects like
smooth muscle contraction changes in cell secretions - DAG activates enzyme protein kinase C (PKC)
- PKC phosphorylates a large number of proteins leading to
cell’s response - lipid portion of DAG is precursor for prostaglandins
10
Q
Describe Calcium calmodulin
A
- hormone interacts with the membrane receptor to
open calcium channels - on entering the cell calcium binds with the
protein calmodulin - once 3-4 of the 4 calcium binding site in calmodulin
are filled it changes shape and initiates multiple effects including activation and inhibition of protein kinases - eg) activates myosin kinase which acts directly on the
myosin of smooth muscle to cause contraction
11
Q
Which hormones have intracellular receptors?
A
- Steroid
- Thyroid
12
Q
How do steroids carry out their intracellular actions?
A
- diffuse across the cell membrane and enter the cytoplasm and binds to the receptor protein
- diffuses/transported into nucleus
- binds on specific points on the DNA strands in chromosomes
- activates the transcription of specific genes to form mRNA
- mRNA diffuses into cytoplasm
- promotes the translation process at the ribosomes to form new proteins
- proteins can be enzymes, transport proteins, or structural proteins
13
Q
How do thyroid carry out their intracellular actions?
A
- T3 and T4 bind directly with receptor proteins in the nucleus
- activate thethe formation of many types of proteins
- enhances intracellular metabolic activity
- once bound, continue to express their control functions for days or even weeks
14
Q
Describe closed loop control of hormone production/release
A
Closed loop control (feedback control) where the hormone regulates its own secretion.
- negative feedback mechanism
- stimulus causes release of hormone
- conditions or products occurring as a result of the hormone action tend to suppress further release of the hormone
- positive feedback
- result in surges of hormones
- biological action of the hormone causes additional secretion of the hormone
15
Q
What effects does GH have on tissue growth/energy utilization? (7)
A
- stimulates growth and metabolism of cells on bone and muscle
- Promotes protein deposition
- Decreased catabolism of protein and amino acids ‘protein sparing effect’
- Enhanced fat utilization for energy
- Decreased carbohydrate utilization
- Stimulates cartilage and bone growth
- GH increased by various conditions that require nutrient partitioning - increased metabolic demands
