Endocrine System Flashcards
What are hormones?
Molecules produced by the endocrine system.
Function of hormones
- Send messages to parts of the body
- Maintain homeostasis
- Regulate body’s processes (hunger, bp, sex drive)
Exocrine Glands
Secrete through ducts to the outside of the body
Ex: digestive enzymes
Endocrine Glands
Lack ducts and secrete hormones into the blood
Endocrine System
Consists of ductless glands scattered throughout the body. These glands secrete hormones which travel through blood to target cells.
- Target cells have receptors for binding with specific hormone
- Regulates or directs particular function
Hydrophilic Hormones
Peptide hormones and catecholamine’s, water loving
Lipophilic Hormones
Steroid hormones and thyroid hormone, lipid loving
Endocrine only function
Pituitary, parathyroid, thyroid, and the adrenal gland
Mixed function
Pineal, hypothalamus, thymus, heart, stomach, pancreas, duodenum, kidney, skin, adipose tissue, ovaries, placenta, and testes
Influences of concentration of hormones in plasma
- Hormone rate of secretion
- Rate of metabolic activation or conversion
- Transport (binding to plasma proteins)
- Inactivation (excretion)
Regulation of secretion
- Negative feedback
- Neuroendocrine reflexes ability of nervous system to regulate secretion
- Diurnal (circadian) rhythms
Endocrine dysfunction
Commonly result from abnormal plasma concentrations of a hormone via inappropriate rates of secreation
Types of endocrine dysfunction
- Hyposecretion
- Hypersecretion
Hyposecretion
Too little hormone is secretion
Primary hyposecretion
Too little hormone is secreted because of abnormality within gland
Secondary hyposecretion
Too little secretion of hormone due to deficiency of its tropic hormone, no problem with gland
Hypersecretion
Too much hormone is secreted
Causes of hypersecretion
- Tumors that ignore normal regulatory input and continuously secrete excess hormone
- Immunologic factors
Primary hypersecretion
Too much hormone is secreted due to abnormality within gland
Secondary hypersecretion
Excessive stimulation from outside the gland causes over-secretion
How can hormones influence activity of another hormone at given target cell?
- Permissiveness
- Synergism
- Antagonism
Permissiveness
One hormone must be present in adequate amounts for full exertion of another hormone’s effect
Synergism
Occurs when actions of several hormones are complimentary
- Combined effect is greater than the sum of their separate effects
Antagonism
Occurs when one hormone causes loss of another hormone’s receptors
- Reduces effectiveness of second hormone
Hypothalamus
Endocrine organ (secretes several hormones); most of them affect the pituitary
Pituitary Gland
Pea-sized gland connected to the hypothalamus via the infundibular stalk
- Posterior pituitary
- Anterior Pituitary
Posterior Pituitary
Neurohypophysis; composed of nervous tissue
Anterior Pituitary
Adenohypophysis; consists of glandular epithelial tissue
What is released from the pituitary gland?
Human growth hormone (hGH)
Adrenocorticotropin (ACTH)
Thyroid stimulating hormone (TSH)
Gonadotropic hormones
- Luteinizing hormone (LH)
- Follicle stimulating hormone (FSH)
Prolactin (PRL)
Vasopressin
Oxytocin
Magnocellular Neurons
Secrete two hormones (neurohormones); vasopressin and oxytocin; synthesized and packaged into vesicles that are transported to posterior pituitary
ADH/Vasopressin
Conserves water during urine formation
Oxytocin
Stimulates uterine contraction during childbirth and milk ejection during breast-feeding
Vasopressin in kidneys
Nephrons in kidneys, increase permeability of distal and collecting tubules to H2O
Vasopressin arterioles
Throughout body, causes constriction
Hypothalamic-Hypophyseal Portal System
System that provides a vascular link to the anterior pituitary from the hypothalamus
Posterior Pituitary Hormones
Vasopressin and oxytocin
Anterior Pituitary Hormones
TSH
ACTH
FSH
LH
GH
PRL
Thyroid-stimulation hormone (TSH)
Stimulates secretion of thyroid hormone
Adrenocorticotropic hormone (ACTH)
Stimulates secretion of cortisol by adrenal cortex
Follicle-stimulating hormone (FSH)
Females: growth and development of ovarian follicles and secretion of estrogen by ovaries
Males: sperm production
Luteinizing hormone (LH)
Females: ovulation and luteinization, ovarian secretion of sex hormones
Males: testosterone secretion
Growth hormone (GH)
Responsible for regulating overall body growth; intermediary metabolism
Prolactin (PRL)
enhances breast development and milk production
Three pathways in which the hypothalamus and pituitary direct neuroendocrine function
- HPA
- HPG
- HPT
HPA
Hypothalamic-pituitary adrenal axis
- Main stress response system
HPG
Hypothalamic-pituitary gonadal axis
- Regulate reproduction
HPT
Hypothalamic-pituitary thyroid axis
- Regulation of metabolism and some stress
Tropic hormones target what?
Other endocrine glands
TRH
TRH –> thyroid gland –> thyroid hormone (T3 and T4) –> increased metabolic rate
CRH (corticotropin-releasing hormone)
CRH –> ACTH –> adrenal cortex –> cortisol
–> metabolic actions; stress response
GH-IH
GH –> Liver (+) –> IGF-I –> bone and soft tissues –> growth
GH-RH
GH –> Adipose tissue, muscle, liver (+ or -)
–> metabolic actions
Adrenal Glands
Embedded above each kidney in a capsule of fat; composed of two endocrine organs
What organs are the adrenal glands made of?
- Adrenal Cortex
- Adrenal Medulla
Adrenal Cortex
Outer portion of adrenal gland that secretes steroid hormones
Adrenal Medulla
Inner portion of adrenal gland that secretes catecholamine’s (epinephrine and norepinephrine)
What layers make up the adrenal cortex?
Zona glomerulosa (mineralocorticoids/aldosterone), zona fasciculata, and zona reticularis (both contain glucocorticoids/cortisol and sex hormones dehydroepiandrosterone)
Mineralocorticoids
Influence mineral balance, specifically Na+ and K+ balance
Glucocorticoids
Glucose, protein and lipid metabolism, and stress hormone
Sex hormones (adrenal cortex)
Most abundant physiologically
Aldosterone
Principal action site on distal and collecting tubules of kidney and regulation of its secretion is largely independent of anterior pituitary control
How is aldosterone secretion increased
- Activation of renin-angiotensin-aldosterone system by factors related to a reduction in Na+ and a fall in blood pressure
- Direct stimulation of adrenal cortex by rise in plasma K+ concentration
Cortisol
Stimulates hepatic gluconeogenesis, inhibits glucose uptake and use by many tissues (but not brain), stimulation protein degradation in many tissues (especially muscle), facilitates lipolysis, plays role in adaptation to stress, can have anti-inflammatory and immunosuppressive effects and pharmacological levels
How is cortisol secretion regulated?
Negative feedback loop involving hypothalamic CRH and pituitary ACTH
Short-term stress response
Stress signal to hypothalamus –> along nerve impulses to spinal cord –> preganglionic sympathetic fibers –> adrenal medulla (secretes amino acid based hormones) –> catecholamines
- Increased heart rate
- Increased blood pressure
- Liver converts glycogen to glucose and releases glucose to blood
- Dilation of bronchioles
- Changes in blood flow patterns leading to decreased digestive system activity and reduced urine output
- Increased metabolic rate
Long-term stress response response
Stress signal to hypothalamus –> CRH release to corticotroph cells of anterior pituitary –>ACTH to target in blood –> adrenal cortex (secretes steroid hormones) –>Mineralocorticoids (retention of Na+ and water by kidneys then increase blood volume and pressure) or Glucocorticoids (proteins and fats converted to glucose or broken down for energy, increased blood glucose, and suppression of immune system)
Adrenal medulla function
- Modified part of sympathetic nervous system
- Primary stimulus for increased adrenomedullary secretion activation of sympathetic nervous system by stress
- Releases epinephrine and norepinephrine which is secreted into blood by exocytosis of chromaffin granules
Epinephrine
- Reinforces sympathetic system in mounting general systemic “fight-or-flight” responses
- Maintenance of arterial blood pressure
- Increases blood glucose and blood fatty acids
Thyroid Gland
Consists of two lobes of endocrine tissue joined in middle by narrow portion of the gland
Cells in thyroid gland
- Follicular cells
- C cells
Follicular Cells
Produce two iodine containing hormones derived from amino acid tyrosine
1. Tetraiodothyronine (T4, thyroxine)
2. Tri-iodothyronine (T3)
C Cells
Secrete peptide hormone calcitonin
Thyroid gland pathway
Hypothalamus releases thyrotropin-releasing hormone (TRH) –> thyroid-stimulating hormone (TSH) –> thyroid gland releases T3 and T4 which results in increased metabolism, growth and development, and increased catecholamine effect –> negative feedback leads to more release of TRH and TSH from hypothalamus and anterior pituitary
Thyroid hormone regulation
Secretion is regulated by negative-feedback system between hypothalamic TRH, anterior pituitary TSH, and thyroid gland T3 and T4; feedback loop maintains thyroid hormones relatively constant
Growth Hormone
Circadian rhythms, stress and cortisol, and fasting impact GHRH and somatostatin in hypothalamus –> release of growth hormone in anterior pituitary –> can go to liver and other tissues that release insulin-like growth factors and then cartilage growth OR to increase in blood glucose and bone and tissue growth
Normal Growth Curve
Includes a postnatal growth spurt and pubertal growth spurt
Bone growth in embryo
Bone starts to replace cartilage
Bone growth in a fetus
Growth in bone length, medullary cavity development, new centers of bone growth
Bone growth in a child
Growth in bone width, epiphyseal plate cartilage, spongy bone, new bone formation
Types of GH abnormalities
- GH Deficiency
- GH Excess
GH Deficiency
- Due to pituitary defect
- Hyposecretion of GH in child is one cause of dwarfism
- Deficiency in adults produces relatively few symptoms
GH Excess
- Most often caused by tumor of GH-producing cells of anterior pituitary
- Symptoms depend on age of individual when abnormal secretion begins
Types of abnormal secretion
- Gigantism
- Acromegaly
Gigantism
Caused by overproduction of GH in childhood before epiphyseal plates close
Acromegaly
Occurs when GH hypersecretion occurs after adolescence
Pancreatic Hormones
Pancreas has endocrine cells calls Islets of Langerhans; local presence of somatostatin decreases secretion of insulin, glucagon, and somatostatin itself
- B (beta) cells
- A (alpha) cells
- D (delta) cells
Beta cells
Site of insulin synthesis and secretion
Alpha cells
Produce glucagon
Delta cells
Pancreatic site of somatostatin synthesis
Insulin
- Anabolic hormone
- Promotes cellular uptake of glucose, fatty acids, and amino acids and enhances their conversion into glycogen, triglycerides, and proteins –> respectively lowers blood concentration of these small organic molecules
- Secretion is increased during absorptive state; primary stimulus for secretion is increase in blood glucose concentration
Diabetes Mellitus
- Most common endocrine disorder
- Prominent feature of elevated blood glucose levels; urine acquires sweetness from excess blood glucose that spills into urine
- Two major types: Type I and Type II
Type I Diabetes
Characterized by lack of insulin secretion
- None or almost no insulin secretion
- Childhood
- 10-20% of diabetics
- Destruction of beta cells
- Treat with insulin injections, dietary management, and exercise
Type II Diabetes
Characterized by normal or even increased insulin secretion but reduced sensitivity of insulin’s target cells
- Normal or exceed normal insulin secretion
- Adulthood
- 80-90% of diabetics
- Reduced sensitivity to insulin’s target cells
- Treat with dietary control and weight reduction, exercise, sometimes oral hypoglycemic drugs
