UNIT 6 - Endocrine system II - select glands Flashcards
Thyroid gland
Location:
●In the anterior neck, inferior to the larynx.
●Made up of two connected lobes lying on either side of the trachea.
Thyroid gland - structure
●Consists of numerous thyroid follicles, which are round structures that make and store T3 and T4.
●Follicles are surrounded by parafollicular cells, which make calcitonin.
Thyroid gland - hormones 2
1- Triiodothyronine T3 and Thyroxine T4
2- Calcitonin
Triiodothyronine T3 and Thyroxine T4 - Hormone of the thyroid gland
Target: Most body cells
Actions:
▪ Increases metabolic rate
▪ Essential for tissue growth and development (esp. of skeletal, nervous, and reproductive systems)
Calcitonin - Hormone of the thyroid gland
Target: skeleton (bone tissue)
Action: Lowers blood calcium (Ca2+) levels.
How?
by stimulating osteoblast activity &
by inhibiting osteoclast activity.
Parathyroid gland
▪ Location
Four small, rounded glands on the posterior surface of the thyroid gland.
▪ Function
Secretes parathyroid
hormone (PTH).
Parathyroid gland
Parathyroid Hormone (PTH):
Targets: bone, kidney, intestine
Actions: Increases blood Ca2+ levels by:
◦ stimulating osteoclast activity
◦ stimulating kidneys to reabsorb more Ca2+ (decreases Ca2+ lost in urine)
◦ stimulating intestine to absorb Ca2+
Pancreas
▪ Location - posterior to stomach; extends from duodenum to spleen.
▪ Structure - composed of
soft lobular tissue with clusters of endocrine cells called pancreatic islets or islets of Langerhans interspersed in exocrine tissue.
Hormones secreated by pancreas
Insulin
Glucagon
Insulin
Targets: Most cells, but especially
Actions: Decreases blood glucose levels by:
◦ promoting uptake and utilization of glucose by cells
◦ promoting the storage of glucose as glycogen (glycogenesis)
◦ promoting conversion of glucose to fat
▪ Secreted by beta (β) cells within the islets.
Glucagon
Target: Liver
Actions: Increases blood glucose levels by:
◦ stimulating breakdown of glycogen to glucose (glycogenolysis)
◦ promoting gluconeogenesis (formation of new glucose from non-carbohydrate sources)
- Secreted by alpha (α) cells within the islets.
Adrenal Gland
Location:
Two glands that sit just above each kidney
Structure:
- Roughly pyramid shaped with an outer cortex and an inner medulla.
- The cortex and medulla function as separate glands.
Adrenal cortex
●Composed of glandular epithelium.
●Regulated by ACTH from anterior pituitary and humoral mechanisms, such as concentration of sodium and potassium in blood.
●Secretes three classes of corticosteroids:
1. mineralocorticoids
2. glucocorticoids
3. gonadocorticoids
Corticosteroids of adrenal cortex: Mineralocorticoids (Aldosterone)
Mineralocorticoids
Target: Kidney
Actions: Aldosterone stimulates the kidneys to:
◦ reabsorb sodium (Na+) and water
◦ excrete potassium (K+)
Overall, this hormone:
◦ Increases blood volume & blood pressure
◦ aids in sodium & potassium balance
What might trigger secretion of this hormone?
A decrease in blood pressure.
Corticosteroids of adrenal cortex - glucocorticoids (cortisol).
▪ Release is stimulated by ACTH from the anterior pituitary.
Target: most cells
Actions:
▪ increases blood glucose by stimulating gluconeogenesis.
At excessive levels:
▪ inhibits inflammation and immune responses
Corticosteroids of adrenal cortex - gonadocorticoids ( androgens & estrogens)
●The amounts secreted are much lower in comparison to the amounts secreted by the ovaries or testes.
●May play a role in onset of puberty and sex drive.
*Androgens = male sex hormones; ex. testosterone
Adrenal Medulla
●Derived from the same fetal tissue as the nervous system.
●Regulated directly by nerve stimulation from the sympathetic nervous system.
●Secretes epinephrine and norepinephrine (the catecholamines) which, along with the sympathetic nervous system, trigger the “fight-or flight” response.
Adrenal Medulla
●Derived from the same fetal tissue as the nervous system.
●Regulated directly by nerve stimulation from the sympathetic nervous system.
●Secretes epinephrine and norepinephrine (the catecholamines) which, along with the sympathetic nervous system, trigger the “fight-or flight” response.
●These hormonal effects of the catecholamines last about 10 times longer than the effects of sympathetic nervous system alone.
Adrenal Medulla
Primary Actions of Catecholamines:
▪ Dilate vessels supplying cardiac & skeletal muscle.
▪ Increase:
blood glucose, heart rate, blood pressure, mental alertness, respiratory and metabolic rates.
Pineal gland:
▪ Located in posterior diencephalon.
▪ Secretes melatonin
▪ Melatonin targets the hypothalamus and makes us drowsy, thus helping to induce sleep.
▪ Overall, helps regulate daily rhythms such as sleep and wakefulness.
Testies
●Located in scrotum.
●Secrete testosterone.
Actions of testosterone:
▪ Promotes maturation &
maintenance of male reproductive organs and secondary sex characteristics.
▪ Involved with sperm production (spermatogenesis).
Ovaries
- Located in pelvic cavity
- Secrete estrogens and progesterone
Estrogens & Progesterone (collectively)
▪ Promote maturation and maintenance of female reproductive organs and secondary sex characteristics.
▪ Help regulate menstrual cycle.
▪ Aid in preparing for & maintaining pregnancy.
Heart
- Located in thoracic cavity
- Secretes atrial natriuretic peptide (ANP)
- ANP targets the kidneys and stimulates Na+ and water excretion in the urine.
●Actions: Overall, this hormone:
◦Decreases blood volume & blood pressure.
What might trigger secretion of this hormone?
An increase in blood preassure.
Kidney
▪ Located in posterior
abdominal cavity.
▪ Secretes erythropoietin.
▪ Actions: Erythropoietin targets the bone marrow to stimulate red blood cell production.
