Lecture 14- Animal hormones Flashcards
What are hormones?
Chemical signals secreted by the cells of the endocrine system into the extracellular fluid
What are endocrine cells?
Cells that secrete hormones
What are target cells?
Cells that have receptors for the hormones secreted by the endocrine system.
What hormones act at a distance?
Circulating hormones
How do circulating hormones enter the system?
Hormones are secreted into the extracellular fluid and can diffuse into the blood
What are the three types of hormone?
Circulating hormones
Paracrine hormones
Autocrine hormones
What cells do paracrine hormones effect?
Cells near the site of release
What cells do autocrine hormones effect?
The cells that released the hormone
Why do paracrine hormones only effect cells near the site of release?
They are released in tiny quantities
Rapidly inactivated by enzymes
Taken up efficiently by local cells
Give an example of a paracrine hormone.
Histamine- a mediator of inflammation
What do autocrine functions do?
Provide negative feedback to control rates of secretion
Give an example of endocrine cells that exist as single, isolated cells within a tissue.
Hormones of the digestive tract are secreted by cells in the stomach and small intestine walls
What is the name given to aggregations of endocrine cells?
Endocrine glands
What are exocrine glands?
Glands that have ducts that carry their product to the surface of the skin or a body passageway that leads out of the body (sweat glands and salivary glands respectively)
When did chemical communication arise?
Early in evolution
Give examples of organisms that use chemical communication.
Plants, sponges, protists.
What do hormones control in arthropods?
Molting and metamorphosis
What are the three chemical groups hormones can be divided into?
- Peptides/polypeptides
- Steroid hormones
- Amine hormones
To what chemical group does the majority of hormones belong to?
Peptides/polypeptides
Give an example of peptide/polypeptide hormones.
Insulin
What are the chemical properties of peptide or polypeptide hormones?
Water soluble, easily transported in blood
Cannot pass lipid rich cell membranes
How do peptide or polypeptide hormones pass cell membranes?
They are packed in vesicles in the cells that make them and released by exocytosis
What are the chemical properties of steroid hormones?
Lipid soluble
Give an example of steroid hormones.
Testosterone and estrogen- derivatives of cholestrol
How are steroid hormones transported?
They are bound to carrier proteins in order to be transported to target cells
What are amine hormones?
Mostly derivatives of the amino acid tyrosine- some are lipid soluble some are water soluble.
Where are hormone receptors found?
The cell surface or cell interior
Where are the receptors for lipid soluble hormones?
Inside the cell interior in the cytoplasm or nucleus
Where are the hormone receptors for water-soluble hormones?
Receptors are large glycoproteins with three domains
What are the three domains of glycoprotein receptor molecules?
- Binding domain (projects outside plasma membrane)
- Transmembrane domain (anchors receptor to membrane)
- Cytoplasmic domain (extends into cytoplasm)
How do most steroids act on a cell?
Altering gene-expression in the cell
How does the cytoplasmic domain initiate the target cells response?
Activates protein kinase or phosphatases which activate or inactivate enzymes in the cytoplasm
Can also alter gene expression
What does the nature of a response to a hormone depend on?
The responding cell and its receptor- one hormone can trigger different responses.
Give an example of a hormone that can cause different responses on different cells.
Epinephrine which triggers fight-or-flight response
What responses does epinephrine cause?
- Heart- stronger and faster
- Constriction of blood vessels in digestive tract (more blood for muscles)
- Less blood flow to skin and kidneys
- Suppresses immune system
- Breaks down glycogen in the liver- a source of energy
What does the pituitary gland do?
Connect nervous and endocrine functions
Where is the pituitary gland found?
A depression at the bottom of the skill, over the back of the roof of the mouth