Upload
bary
View
42
Download
0
Embed Size (px)
DESCRIPTION
Endocrine System: all an animals hormone secreting cells. Chemical Signals. Categories of Signals Chemical signals that are secreted into the circulatory system and communicate regulatory messages to the body: between individuals between body parts between cells. The Action of Hormones . - PowerPoint PPT Presentation
Citation preview
Endocrine System: all an animals hormone secreting cells
Chemical Signals•Categories of Signals •Chemical signals that are secreted into the circulatory system and communicate regulatory messages to the body: •between individuals•between body parts•between cells
The Action of Hormones
• The Action of Hormones (between body parts)• A hormone does not seek out a target organ; the organ is awaiting the arrival of the hormone.•Different cells/organs have specialized receptors that recognize specific hormones•Steroid hormones •Peptide hormones
Target Cell Concept
Action of Hormones•Chemical signals produced by one cell that
regulate the metabolism of other cells• Steroid Hormones -Can cross cell membranes• Peptide Hormones• Most bind to receptor in plasma membrane• First Messenger
• Causes internal release of cAMP • Second Messenger
Review of Cell Signaling
1. Reception: target cell detection 2. Transduction: single-step or series of changes3. Response: triggering of a specific cellular response
Steroid hormones are lipids and cross cell membranes freely
Hormone-receptor complex binds to DNA resulting in activation of genes that produce enzymes
Peptide hormones never enter a cell so they bind to a receptor protein in plasma membrane.
Examples of Hormone Activity
Different activity for same hormone•Many times hormones can elicit a myriad
of responses. The same hormone can activate different receptors on different cell types to elicit several responses• In each case, there is some sort of signal
transduction pathway, but with a different effect• Example: Release of epinephrine in the
“fight or flight” response
The Action of Hormones• The Action of Hormones (between cells)• Paracrine signaling is the term given to hormone
signaling, locally, between cells• Release of a hormone can activate neighboring cells in
seconds (much quicker response than body to organ – long distance signaling)
• Examples:• Cytokines (remember immune system)• Growth factors (stimulate cell growth and
differentiation – after a cut or broken bone)• Nitric Oxide (improves blood flow by vasodilation when
low O2 levels are sensed)• Prostaglandins (general group of modified fatty acids
that modify neighboring cells depending on cell type)
Homeostasis• Endocrine system is especially involved with homeostasis.• Effect of hormones is controlled in 3 ways:•Negative Feedback • Stops release of hormone
• Postivie Feedback • Enhances hormone release• Antagonistic hormones• Hormones have opposing (or opposite) effect
Homeostasis• Negative feedback (ex.)• Pancreas produces insulin when blood
glucose rises; this causes liver to store glucose.
• When glucose is stored, level goes down and pancreas stops insulin production.
• Positive feedback (ex.)• Oxytocin stimulates uterine muscle contractions during
birth• As more contractions occur, more oxytocin is released
• Antagonistic hormones (ex.)• Effect of insulin is offset by glucagon• Thyroid lowers blood calcium level;
parathyroids raise blood calcium level.
Negative Feedback• All body cells utilize glucose;
therefore, its level must be closely regulated.• Beta cells secrete Insulin• Secreted when blood glucose
level is high after eating• Alpha cells secrete
Glucagon• secreted between meals in
response to low blood glucose level.
pancreas & insulin.ram
Positive Feedback•Oxytocin is also made in hypothalamus & stored in posterior pituitary.• Oxytocin • stimulates uterine muscle contraction • stimulates release of milk from mammary glands
• This positive feedback increases intensity; positive feedback does not maintain homeostasis.
Antagonistic hormones• Thyroid hormones increase metabolic rate; there is no one target organ, all organs respond • Thyroid gland also produces calcitonin• Calcitonin lowers calcium level in blood and increases deposit in bone by reducing osteoclasts.• Low calcium levels stimulate release of parathyroid hormone (PTH) from the parathyroid gland
• The two hormones (calcitonin and parathyroid hormone) counteract the effects of the other
What type of regulation?•Antidiuretic hormone (ADH) promotes reabsorption of water from collecting ducts in kidneys.• Nerve cells in the hypothalamus determine when blood is too concentrated; ADH is released and kidneys respond by reabsorbing water.• As blood becomes dilute, ADH is no longer released•What type of feedback is this?
•NEGATIVE FEEDBACK
Example: Hormone Disease• Diabetes mellitus is a common disease where body
cells do not take up or metabolize sugar.• Liver is not storing glucose as glycogen & cells are
not utilizing glucose for energy.• Type I (insulin-dependent) diabetes - pancreas
does not produce insulin (autoimmune disease: immune system destroys insulin producing beta-cells in the pancreas a.k.a. islet cells)• type II (noninsulin-dependent) diabetes - usually
occurs in obese & inactive individuals of any age. Cells do not respond to insulin