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Anatomy & Physiology: Week Six
Chapter 14: The Endocrine System
Endocrine Glands
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Ductless glands
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Secrete hormones
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Widely distributed throughout the body
Hormones
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Chemical messengers that influence or control activities of other tissues and organs
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Classification
- Proteins (and protein-related substances
- Steroids
Hormone Targets
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Many target tissues result in more widespread effects
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With fewer target tissues come fewer effects
Click to review labeling the endocrine glands
Control of Hormone Secretion
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Feedback: Negative or Positive
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Biorhythms: Circadian and monthly
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CNS: Psychoneuroendocrinology
Control by Negative Feedback Loop
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Example: As level of cortisol rises in the blood to needed level, cortisol shuts off further secretion of ACTH
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As level of cortisol drops, inhibition is relieved
Control by Positive Feedback Loop
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A bodily change stimulates further change in the same direction.
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The following are some examples:
- During labor, pressure of baby's head on cervix stimulates release of oxytocin.
- Oxytocin stimulates uterine contraction, further increasing pressure on cervix.
- More oxytocin is released until delivery.
Pituitary Gland and the Hypothalamus
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Hypothalamus controls pituitary function.
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Connected to anterior pituitary through capillaries and to posterior pituitary through tissue extension,
Pituitary Gland: Two Parts
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Anterior pituitary (adenohypophysis) controlled by releasing hormones of the hypothalamus.
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Posterior pituitary (neurohypophysis) extension of the hypothalamus.
Hormones of the Anterior Pituitary Gland
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Tropic hormones: TSH, ACTH, Growth hormone, FSH, LH, Prolactin
Hormones of the Posterior Pituitary Gland
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Antidiuretic hormone, Oxytocin
Click to review pituitary hormones
Thyroid Gland: Hormones
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Follicular cells secrete T3 and T4
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regulates metabolism
- Permit proper function of all other hormones
- Promote normal maturation of the nervous system
- Promote normal growth and development
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Parafollicular cells secrete calcitonin
- Helps regulate calcium levels in the blood,
- Stimulates osteoblastic activity
Abnormal Thyroid Function
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Hypothyroidism: Deficiency of T3/T4, results in a slowed-down metabolic rate or myxedema.
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Hyperthyroidism: Excess of T3/T4, causes accelerated metabolic rate or Graves' disease.
The Need for Iodine
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T3 = triodothyronine
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T4 = tetraiodothyronine (thyroxine)
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Iodine is essential for synthesis of T3 and T4
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Iodine deficiency causes goiter or enlargement of the thyroid gland
Click to study Chapter 14
Vocabulary words
Four Parathyroid Glands
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Lie along posterior wall of the thyroid gland
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Are most important regulator of blood calcium
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Secrete parathyroid hormone (PTH), which elevates blood calcium
- Bone - resorption
- Kidney - reabsorbs Calcium ions from urine
- Intestine - absorbs dietary calcium ions
Parathyroid Glands: Abnormal Secretions
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Hyposecretion: Hypocalcemic tetany, causing carpal spasm
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Hypersecretion: Hypercalcemia, "Bones. stones, moans, and groans."
Adrenal Glands
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Located above the kidneys
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Adrenal medulla: inner region secreting catecholamines
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Adrenal cortex: outer region secreting steroids
Adrenal Medulla
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Extension of sympathetic nervous system.
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Fight-or-flight response
- Increases heart rate and blood pressure
- Mobilizes body for emergencies
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Catecholamines: epinephrine and norepinephrine
Adrenal Cortex: Steroids
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Sugar: Glucocorticoids - convert amino acids into glucose (gluconeogenesis) and help maintain blood glucose levels between meals. Affects protein and fat metabolism, burning both substances as fuel to increase energy production.
- Cortisol, most important
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Salt: mineralocorticoids - plays an important role in the regulation of blood volume, blood pressure, and the concentration of electrolytes. Primary target is the kidneys. Stimulates the reabsorption of salt and water and excretion of potassium.
- Aldosterone
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Sex: Sex hormones -
- Female: estrogens
- Male: androgens, testosterone, most important
Click to review the glands and their hormones
Pancreas
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Across upper abdomen
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Islets of Langerhans secrete hormones
- Alpha cells secrete insulin
- Beta cells secrete insulin
Pancreas Regulates Blood Glucose
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Blood glucose levels rise, pancreas secretes insulin.
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Blood glucose level falls, pancreas secretes glucagon
Insulin in Normal Metabolism
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Carbohydrate
- increased transport of glucose into cell
- Use of glucose as fuel
- Storage of excess glucose as glycogen
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Protein
- Stimulation of protein synthesis
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Fat
- Stimulation of fatty acid synthesis
Deficiency of Insulin
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Called diabetes mellitus
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Has devastating effects if left untreated
Glucagon
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Pancreatic hormone secreted by alpha cells of the islets of langerhans
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Primary action is to increase blood glucose
Other Glands
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Gonads
- Testes secrete testosterone
- Ovaries secrete progesterone and estrogen
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Thymus
- Secretes thymosins
- Affects immune function
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Pineal Gland
- Secretes melatonin
- Affects biological clock
Other Hormones
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Organ-specific hormones
- Secreted by organs such as heart, kidney, digestive organsd
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Prostaglandins
- Secreted by most tissues
- Most act locally
- Play a role in regulation of smooth muscle contraction, inflammatory response, and pain.
Click to review the hormones and their functions
Click to review week six homework
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