Endocrine System (Flashcards)
What does the endocrine system regulate?
The endocrine system regulates growth, reproduction, and metabolism. It regulates long-term events
Where can receptors be found?
Receptors are proteins that can be found on the cell membrane or intracellularly (in the nucleus)
How do hormones travel to target cells?
Glands and tissues secrete hormones, which travel in the blood to target cells. Hormones bind to receptors on target cells and change cell activity.
How do water-soluble hormones act on target cells?
Water-soluble hormones bind to receptors on the cell membrane because they cannot cross the hydrophobic areas of the phospholipid bilayer. They act as “1st messengers” in a signaling cascade
Describe the mechanism of action of water-soluble hormones.
- The hormone binds to the cell membrane receptors
- The hormone-receptor complex activates membrane proteins like G-proteins
- Membrane proteins activate 2nd messenger systems (e.g., cAMP, Ca2+)
- cAMP activates protein kinases, which then alter the activity of other proteins by phosphorylating them.
Give an example of a second messenger system.
- Using cAMP (cyclic adenosine monophosphate) as a second messenger:
- A hormone binds to a cell-surface receptor and activates a G-protein
- The G-protein activates adenylate cyclase (a membrane protein)
- Adenylate cyclase converts ATP to cAMP, increasing cAMP concentration in the cytosol
- cAMP activates protein kinases in the cytosol
- Protein kinase acts on other proteins to alter cell activity
Why are 2nd messenger systems used?
- The hormone can’t enter the cell (water soluble)
- They are rapid acting (enzymes are already present and just need activation)
- One hormone molecule activates many enzyme molecules (cascade), which multiplies the signal
- The messenger is broken down or removed, limiting the signal
How do lipid-soluble hormones act on target cells?
Lipid-soluble hormones, like steroids and thyroid hormones, enter the target cell and bind to intracellular (nuclear) receptors in the cytosol or nucleus. This triggers protein synthesis and gene transcription.
Describe the mechanism of action of lipid-soluble hormones.
- The hormone enters the target cell and binds to intracellular receptors in the cytosol or nucleus
- The hormone-receptor complex binds to a specific region on DNA, activating genes and starting gene transcription to produce messenger RNA (mRNA)
- mRNA attaches to ribosomes to produce proteins (translation).
What are the three types of stimuli that can trigger hormone secretion?
Humoral, neural, and hormonal stimuli
Describe humoral stimulus.
The stimulus for hormone release is a change in the concentration of a particular ion or nutrient in the blood. For example, increased blood glucose leads to insulin release
Describe neural stimulus.
Neural stimulus gives the example of heart rate and uterine contractions
What are the three phases of the General Adaptation Syndrome?
- Phase 1:
- Alarm Reaction (Fight or Flight Response)
- Phase 2:
- Resistance Reaction
- Phase 3:
- Exhaustion
Define stress and General Adaptation Syndrome (GAS).
Stress is any extreme external or internal stimulus. GAS is a set of body changes coordinated by the hypothalamus in response to stress
Briefly describe the alarm reaction (Phase 1 of GAS).
This is an immediate response coordinated by the nervous system. It involves increased blood glucose, heart rate, respiration rate, and blood flow to skeletal and cardiac muscles and the brain, along with decreased blood flow to the skin and abdominal viscera, and reduced digestion and urine production
Briefly describe the resistance reaction (Phase 2 of GAS).
This is a long-term response coordinated by the endocrine system to permit recovery or respond to longer-term stress. Hypothalamic hormones initiate this phase, leading to increased blood glucose and the use of fats for energy.
Briefly describe the exhaustion phase (Phase 3 of GAS).
Exhaustion results from the depletion of body resources, loss of K+, and damage to organs.
What are the functions of testosterone?
- Testosterone functions include:
- Development of organs of the reproductive tract and secondary sex characteristics.
- Stimulation of bone growth at the epiphyseal plate.
- Promotion of protein anabolism.
- Direct stimulation of spermatogenesis.
What are the functions of FSH (Follicle Stimulating Hormone) in females?
FSH stimulates primary follicles to become secondary follicles. It is inhibited by progesterone.
What are the functions of LH (Luteinizing Hormone) in females?
LH stimulates estrogen production from theca and granulosa cells of the follicle. A surge in LH causes ovulation and the formation of the corpus luteum.
What are the functions of estrogen?
Estrogen is required for ovulation. It promotes the development of secondary sex characteristics, stimulates the growth and maintenance of the endometrium, and stimulates bone growth during puberty.
What are the functions of progesterone?
Progesterone prepares the uterus for pregnancy.
What happens during the follicular phase of the ovarian cycle (days 1-14)?
FSH stimulates primary follicles to become secondary follicles, which secrete estrogen, causing blood estrogen levels to rise.
What occurs during the luteal phase of the ovarian cycle (days 15-28)?
High progesterone levels from the corpus luteum inhibit GnRH, LH, and FSH, preventing the development of new follicles.
What are the effects of oral contraceptives?
Oral contraceptives contain high levels of estrogen and progesterone, which inhibit GnRH secretion, resulting in low FSH and LH levels. This prevents follicle maturation and ovulation.
