Chapter 16 Highlights Flashcards
How do hormones send their signals?
- Secretes into blood to affect distant targets
- AKA classic endocrine signals
Paracrine
- Chemicals secreted by cells into extracellular space
- Affects nearby but different types of cells
Autocrine signals
- Chemicals secreted by cells into interstitial fluid
- Elicits effects from same cell or cell type
Main groups of hormones
- Amino acid derivatives
- Peptide hormones
- Lipid derivatives
Amino acid derivatives
Small molecules structurally related to individual amino acids
Peptide hormones
Chains of amino acids
Lipid derivatives
Molecules structurally related to lipids
Where do single amino acid or polypeptide hormones stay?
Outside the cell
What do single amino acid or polypeptide hormones need to activate enzymes inside the cell?
- G proteins
- Second messengers
Classification of hormones
- Amino-acid hormones
- Steroid hormones
Amino-acid hormones
- 1 amino acid = amine hormones
- Multiple amino acids = peptide hormones
- Complete proteins = protein hormones
- Generally considered hydrophilic
What do hydrophilic hormones bind to?
Bind to plasma membrane receptors
Steroid hormones
- Developed from cholesterol
- Hydrophobic hormones
Hydrophobic hormones
- Can cross the plasma membrane
- Binds to receptors in cytosol or nucleus
- Forms a complex with its receptor
- Generally interacts with DNA of target cell
- Effects by changing rate of protein synthesis
Pituitary gland
- Small organ
- Sits in sella turcica of sphenoid
2 structurally and functionally distinct components of pituitary gland
- Anterior pituitary
- Posterior pituitary
Anterior pituitary
- Adenohypophysis
- True gland
- Hormone-secreting glandular epithelium
Posterior pituitary
- Neurohypophysis
- Nervous tissue
Hypothalamic-hypophyseal portal system
- Specialized blood supply
- Allows both hypothalamus and pituitary to deliver hormones directly to target cells
What kind of blood vessels merge in hypothalamus
- Tiny capillaries
- They eventually form larger portal veins that travel through infundibulum
Where to the portal veins lead?
To a second group of capillaries in anterior pituitary gland
Portal system
A system in which capillaries are drained by veins that lead to another set of capillaries
Are any hormones made in posterior pituitary?
- No
- 2 neurohormones are produced by hypothalamus and then stored and released from posterior pituitary
Neurohormones produced by hypothalamus and stored in posterior pituitary
- Antidiuretic hormone (ADH)
- Oxytocin
Function and production of antidiuretic hormone (ADH)
- Controls water balance
- Produced continually in low amounts by hypothalamus neurons
How is ADH transported?
- Through axons in infundibulum to axon terminals in posterior pituitary
- Then stored in synaptic vesicles
Do the axon terminals in posterior pituitary have synapses?
- Do not have synapses
- Instead releases ADH into blood vessels when stimulated by action potentials
Aquaporins
ADH allows for insertion of water channels called aquaporins into plasma membranes of kidney tubule cells
What happens to the water in aquaporins?
- Water first passes into cytosol of cells
- Proceeds back into the extracellular fluid
- Moves into the blood, otherwise would have been eliminated from body in urine
Diabetes insipidus
- Caused by lack of ADH secretion or activity
- Causes extreme thirst and signs of dehydration
- Body is unable to conserve most water consumed
Oxytocin
- Produced by hypothalamus
- Stored in axon terminals of posterior pituitary gland
Function of oxytocin
- Primary focused on reproduction
- Target cells are in mammary glands of breast tissue and smooth muscle of uterus
What stimulates oxytocin release in nursing mothers?
- Suckling
- Causes mammary glands to contract, resulting in milk ejection
Milk let-down reflex
- Positive feedback loop
- Suckling induces lactation, causing more suckling and more milk to be released
- Loop ceases when satisfied infant stops suckling
How does the hypothalamus control the anterior pituitary?
- Hypothalamus produces and releases tropic hormones
- Either stimulates or inhibits release of hormones
Transport of tropic hormones
Travels via the hypothalamic-hypophyseal portal system
What kind of hormones are many anterior pituitary hormones?
- Tropic
- Control secretion of hormones by various endocrine glands in body
First tier hypothalamic control
Neuroendocrine cells of hypothalamus secrete releasing and inhibiting hormones in response to change in homeostatic variable (tropic hormones)
Second tier hypothalamic control
- Tropic hormones’ effect on anterior pituitary
- Stimulates or inhibits anterior pituitary hormone secretion
Third tier hypothalamic control
- Actions of anterior pituitary hormones at target tissues
- Target tissue glands secrete hormones that can affect various homeostatic variables
Divisions of the anterior lobe
- Pars distalis
- Pars intermedia
- Pars tuberalis
Pars distalis
- Secretes 6 hormones, 4 are tropins
- Growth hormone (GH)
- Thyroid-stimulating hormone (TSH) tropic
- Adrenocorticotropic hormone (ACTH) tropic
- Follicle-stimulating hormone (FSH) tropic
- Luteinizing hormone (LH) tropic
- Prolactin (PRL)
Pars intermedia
Secretes 1 hormones (MSH)
Anterior pituitary hormones that affect other glands
- Luteinizing hormone
- Follicle-stimulating hormone
- Prolactin
Luteinizing hormone effect on men
Stimulates production of testosterone by testes under direction of hypothalamic gonadotropin-releasing hormone (GnRH)
Luteinizing hormone effect on women
- Stimulates production of estrogen and progesterone from ovaries
- Triggers release of oocyte in ovulation
- Also under direction of GnRH
Follicle-stimulating hormone effect on men
- Stimulates cells of testes to produce chemicals that bind and concentrate testosterone
- Under direction of GnRH
Follicle-stimulating hormone effect on women
- FSH and LH together trigger production of estrogen
- FSH also triggers maturation of ovarian follicles (house developing oocytes)
Prolactin
- Stimulates growth of mammary gland tissue
- Initiates milk production after childbirth
- Maintains milk production during breastfeeding
What stimulates release of prolactin?
- Release stimulated by hypothalamic prolactin-releasing hormone
What inhibits release of prolactin?
- Release inhibited by prolactin-inhibiting factor (dopamine)
What is the effect of growth hormone?
Stimulates cell growth and replication through release of somatomedins or IGF (insulinlike Growth Factors)
What stimulates the release of growth hormone?
Hypothalamus –> Growth-hormone releasing hormone (GH-RH)
What inhibits the release of growth hormone?
Hypothalamus –> Growth-hormone inhibiting hormone (GH-IH)
What cells are most sensitive to growth hormone?
Skeletal muscle and cartilage cells
What role does the liver play with growth hormone?
- Liver stimulates IGF
- IGF binds to cells and increases rate of amino acid production to make proteins
Effects of growth hormone?
- Breakdown of fat
- Breakdown of stored glycogen in liver
What happens when growth hormone stimulates the breakdown of fat?
- Fats breakdown
- Fatty acids increase in blood
- Greater use by tissues
- Decreased glucose consumption leads to a glucose-sparing effect
What happens when growth hormone stimulates the breakdown of glycogen?
- Glycogen breakdown
- Increased glucose in the blood
- Increased glucose can have diabetogenic effect (can lead to an endocrine disorder)
Hypothalamic hormones which regulate growth hormone
- Growth hormone-releaseing hormone
- Hypothalamic somatostatin
When does growth hormone-releasing hormone secretion increase?
During exercise, fasting, stress, and after ingestion of protein-rich meal
Growth hormone disorders
- Giantism
- Acromegaly
- Pituitary dwarfism
Giantism
- Hypersecretion of GH BEFORE epiphyseal plate closure
- Leads to extremely tall people
- Also increases size of other tissues (heart)
Acromegaly
- Hypersecretion of GH AFTER epiphyseal plate closure
- Progressively distorts organs
- Can lead to heart failure
What body parts are most affected by acromegaly?
Tissues of head, face, hands, feet, liver, and heart
Pituitary dwarfism
- Hyposecretion of GH
- Leads to short, but proportional, individuals
What does the thyroid gland secrete?
- Thyroid hormone
- Calcitonin
Parafollicular (C) cells
- Neuroendocrine cells in the thyroid
- Secrete calcitonin
What does calcitonin do?
- Reacts to calcium concentration in the blood
- Acts to decrease calcium concentration
- Decreases osteoclast activity
- Lengthens life span of osteoblasts
What is the microscopic composition of the thyroid and parathyroid glands?
- Thyroid follicles (multiple spheres)
- Follicle cells at outer edge of follicles produce and secrete thyroid hormones
Colloid
Protein-rich, gelatinous material
What do colloids contain?
- Precursor for thyroid hormone and a high concentration of iodine atoms
- Both are important to thyroid hormone synthesis
Parafollicular cells
- In spaces between adjacent thyroid follicles
- Large cells that produce calcitonin
Parathyroid glands
- Typically 3-5 separate glands
- On posterior surface of thyroid gland
What do parathyroid glands secrete?
Parathyroid hormone from chief cells
Chemical structure of thyroid hormone
Amino acid core bound to either 3 or 4 iodine atoms
Amino acid core bound to 3 iodine atoms
- Triiodothyroxine
- T3
Amino acid core bound to 4 iodine atoms
- Thyroxine
- T4
Enzyme responsible for making T3 and T4
Thyroid peroxidase
Thyroglobulin
- Large thyroid hormone precursor protein
- Secrete by follicle cells into colloid
Relationship between iodine and TSH
TSH stimulates iodine to be pumped (ion pump) into the follicle cell
Where are iodide ions secreted into?
Colloid
What are iodide ions converted into?
Iodine atoms that attach to thyroglobulin by thyroid peroxidase
Thyroid follicles
-
First tier of T3 and T4 control
Thyrotropin-releasing hormone (TRH) is released from hypothalamus
Second tier of T3 and T4 control
Thyroid stimulating hormone (TSH) is released from anterior pituitary gland
What does thyroid-stimulating hormone do?
- Stimulates iodine to be pumped into the follicle cell
After stimulating iodine to be pumped, what does thyroid peroxidase do?
It produces T3 and T4 and attaches to thyroglobulin
Third tier of T3 and T4 control
Release of T3 and T4
What inhibits secretion of TRH and TSH?
- Rising levels of free T3 and T4
- Somatostatin
Common thyroid disorders
- Hyperthyroidism
- Hypothyroidism
Symptoms of hyperthyroidism
- Weight loss
- Heat intolerance
- Disruptions in blood pressure and heart rhythm
- Development of goiter and exophthalmos
Goiter
Enlargement of thyroid gland
Exophthalmos
Protruding eyeballs
Graves’ disease
- Most common hyperthyroidism
- Immune system produces abnormal proteins that mimic actions of TSH on thyroid gland
Symptoms of hypothyroidism
- Weight gain
- Cold intolerance
- Slow heart rate
- Low BP
- Goiter
Possible reasons for hypothyroidism
- Immune system disorder
- Lack of available iodine
Congenital hypothyroidism
- Cretinism
- Develops when infant is born with inadequate thyroid function
What happens when cretinism is present?
- Can lead to physical and nervous system development delays
- Can lead to potential mental retardation if left untreated
What cells secrete parathyroid hormone (PTH)?
Chief cells
What does parathyroid hormone affect?
Maintenance of blood calcium ion concentration
What is parathyroid hormone secreted in response to?
Declining calcium ion levels in blood
What are the effects of parathyroid hormone?
- Increases release of calcium ions from bone by stimulating osteoclast activity
- Increases absorption of dietary calcium ions by small intestine
Where are the adrenal glands located?
Superior aspect of each kidney
Describe the shape of the adrenal glands
Roughly pyramid-shaped
What do the adrenal glands produce?
- Catecholamine
- Steroid hormone
Regions of adrenal glands
- Cortex
- Medulla
Cortex of adrenal gland
- Outer region
- Typical endocrine gland with functions similar to what has already been discussed
Medulla of adrenal gland
- Inner region
- Neuroendocrine organ that secretes neurohormones
Hormones secrete by the adrenal cortex
- Aldosterone
- Cortisol
- Androgens
Cells that secrete aldosterone
Densely packed cells
Cells that secrete cortisol and androgens
Cells stacked on one another in columns
Cells that secrete epinephrine and norepinephrine
Thin layer of cells arranged loosely in clusters
Zones of the adrenal cortex
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
Hypothalamic-pituitary-adrenocortical (HPA) axis
Multi-tiered negative feedback loop which partially regulates the adrenal cortex
Functions of aldosterone
- Regulates concentration of sodium and potassium ions in the body
- Regulates extracellular fluid volume
- Maintains BP
- Maintains acid-base homeostasis
How does aldosterone regulate concentration of sodium and potassium ions in the body?
Ion gradients are important for function of muscle cells and neurons
How does aldosterone regulate extracellular fluid volume?
- Creates concentration gradient
- Favors movement of water from fluid in the tubules to extracellular fluid and blood
How does aldosterone maintain BP?
- Maintains blood pressure through complex series of interactions called renin-angiotensin-aldosterone system (RAAS)
- Increases BP
- Preserves blood flow to hear, brain, and kidneys
How does aldosterone maintain acid-base homeostasis?
- Activates hydrogen ion pumps in cells of kidney tubules
- Pumps transport hydrogen ions from extracellular fluid into fluid of tubules
What happens to the hydrogen ions after they are pumped into the kidney tubules?
- Excreted in urine
- This lowers pH of blood
- Preserves slightly alkaline pH
Aldosterone disorders
Hyperaldosteronism
What disorders can hyperaldosteronism lead to?
- Hypokalemia
- Hypernatrmia
- Hypertension
Hypokalemia
Low blood potassium ion level
Hypernatrmia
High blood sodium ion level
Hypertension
High blood pressure
Glucocorticoids
Produced in zone fasciculata and zona reticularis
What is the role of glucocorticoids?
Mediate body’s response to stress
Cortisol
- Hydrocortisone
- Most potent glucocorticoid
Stress response
Events that maintain homeostasis when the body is faced with a stressor
What role does cortisol play in the stress response
Regulates of blood glucose levels by cortisol
What happens when cortisol stimulates liver cells?
- Synthesizes enzymes of gluconeogenesis
- Increases blood glucose levels
Effects of the stress response
- Proteins breakdown –> amino acids can be converted to glucose
- Adipocytes release fatty acids –> converted into ATP or glucose in liver
- Decreases levels of certain leukocytes –> anti-inflammatory agent
First tier of cortisol regulation
- CRH secreted daily from hypothalamus in rhythmic fashion
- Peak CRH levels generally in morning
Second tier of cortisol regulation
CRH stimulates ACTH release from anterior pituitary
Third tier of cortisol regulation
ACTH stimulates cortisol production and secretion from adrenal cortex
Elevated cortisol levels suppress the release of what?
- Corticotropin-releasing hormone (CRH)
- Adrenocorticotropic hormone (ACTH)
What does elevated cortisol levels do to the HPA axis?
Closes the negative feedback loop
Cushing’s disease
- Oversecretion from adrenal cortex, usually from tumor
- Can result in moon facies (round face)
- Back of neck producing “buffalo hump”
Latrogenic Cushing’s syndrome
Disorder caused by long-term administration of glucocorticoid-containing products
Addison’s disease
- Hyposecretion from adrenal cortex
- Results in decreased glucose and Na+ levels
- Weight loss, severe dehydration, and hypotension
Androgenic steroids
- Steroid sex hormones that affect reproductive organs as well as other tissues
- Can be converted in circulation to androgen testosterone or female hormone estrogen
Hormones of the adrenal medulla
- Epinephrine (catecholamine)
- Norepinephrine
What are chromaffin cells derived from?
Nervous tissue
What do chromaffin cells secrete?
Epinephrine (catecholamine)
What kind of responses do chromaffin cells elicit?
They mediate immediate responses to stressor
What effects do chromaffin cells have?
- Increase rate and force of heart contraction
- Dilate bronchioles in lung
- Constrict blood vessels supplying skin, digestive organs, and urinary organs
- Dilate blood vessels supplying skeletal muscles
- Dilate pupils
- Decrease digestive and urinary functions
Cell types in pancreas
- Alpha cells
- Beta cells
- Delta cells
Pancreatic islets
- Islets of Langerhans
- Small rounded islands populated by endocrine cells
- Secrete hormones into the bloodstream
What cells secrete glucagon?
Alpha cells
What are the major target tissues of glucagon?
- Liver cells
- Muscle tissue
- Adipose tissue
What kind of reactions does glucagon promote?
Reactions that increase levels of glucose and metabolic fuels in blood
Insulin is the antagonist of what hormone?
Glucagon
Where is insulin produced?
Beta cells of pancreatic islets
What responses does insulin stimulate in target cells?
- Uptake and storage of ingested nutrients
- Lowers blood glucose levels
- Synthesis of glycogen in liver
- Synthesis of fat from lipids and carbs
- Promotes satiety (feeling of fullness)
What causes type I diabetes?
Destruction of beta islet cells
What is the mechanism of type I diabetes?
- Target cells are unable to take in circulating glucose
- Glucose is overproduced in liver because of unopposed actions of glucagon
- Glucagon also elevates level of ketone bodies in blood
What are the effects of type I diabetes?
- Glucose and ketones in urine
- Draws water from ECF by osmosis
- Causes polyuria and polydipsia
Polyuria
Frequeny urination
Polydipsia
Excessive thirst
What causes type II diabetes?
- Insulin’s target tissues become insensitive to insulin
- Target cells do not respond properly to blood glucose concentration
What are the results of type II diabetes?
Hyperglycemia
Signs and symptoms of hyperglycemia
- Glucosuria
- Polyurai
- Polydipsia
Glucosuria
Glucose in the urine
Pineal gland
Primary endocrine component of epithalamus (posterior region of diencephalon of brain)
What effect does melatonin have?
- It is related to light and dark cycles
- Secretion increases in the dark
- Appears to adjust sleep/wake cycle in some individuals
- Inhibits GnRH secretion from hypothalamus
What tissues does melatonin target?
Sleep-regulation centers
Where are the sleep-regulation centers located?
Reticular formation of brainstem
Thymus
- Primary endocrine gland in mediastinum
- Located where T lymphocytes mature
What hormones does the thymus secrete?
- Thymosin
- Thymopoietin
What is the function of thymosin and thymopoietin?
Paracrine signals that assist in T lymphocyte maturation
Primary male and female reproductive organs
- Testes (male)
- Ovaries (female)
Target tissues of testosterone
- Male reproductive organs
- Multiple other target tissues
Effects of testosterone
- Androgenic effects
- Anabolic effects
Target tissues of estrogen
Female reproductive organs
Effects of estrogen
- Development of female secondary sex characteristics
- Regulation of menstrual cycle
- Multiple other effects
Target tissues of progesterone
Multiple other target tissues
Effects of progesterone
- Prepares the body for pregnancy
- Support fetal development
- Multiple other effects
Where do males produce a small amount of estrogen?
In adrenal glands
When does progesterone secretion peak?
After ovulation and during pregnancy
What hormones does adipose tissue produce?
- Leptin
- Resistin
- Adiponectin
Leptin
- Appetite control
- Prevents overfeeding
- Stimulates increased energy expenditure
Can leptin cross the blood-brain barrier
Yes
What neurons does leptin interact with?
Hypothalamic neurons
Resistin
Insulin antagonist
Adiponectin
Enhances sensitivity to insulin
Where are enteroendocrine cells located?
Gastrointestinal tract
What hormones do enteroendocrine cells produce?
- Gastrin
- Secretin
- Cholecystokinin
- Serotonin
Function of Gastrin
Stimulates release of HCl
Function of Secretin
Stimulates liver and pancreas
Function of Cholecystokinin
Stimulates pancreas, gallbladder, and hepatopancreatic sphincter
Function of Serotonin
Acts as paracrine
Osteocalcin
- Prods pancreas to secrete more insulin
- Restricts fat storage
- Improves glucose handling
- Reduces body fat
What activates osteocalcin?
Insulin
Are osteocalcin levels high or low in type II diabetes
- Low
- Increasing levels may be new treatment
Cholecalciferol
Precursor of vitamin D
What causes atrial natriuretic peptide (ANP) secretion?
When increased blood volume stretches stretch-sensitive ion channels
What is the effect of atrial natriuretic peptide?
- Relaxation of smooth muscle cells in blood vessels (vasodilation)
- Natriuresis
- Enhances water excretion from kidneys
Natriuresis
- Enhancing excretion of sodium ions from kidneys
- Creates concentration gradient that water follows into kidney fluid by osmosis
What effect does vasodilation and natriuresis have?
- Decrease blood volume
- Lower BP
What hormones do the kidneys secrete?
- Erythropoietin (EPO)
- Renin
Renin
- Converts plasma protein angiotensinogen to angiotensin I
- Maintains blood pressure
