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Questions and Answers
Which system uses chemical messengers called hormones that are released into the blood?
What is the function of pheromones?
Modify behavior and physiology of other individuals in the same species.
Water-soluble hormones include proteins and peptides.
True
Steroid hormones are made from ____________.
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Match the following components with their descriptions:
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What hormone is secreted by the pineal gland and is believed to play a role in establishing the body's day-night cycle?
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High levels of melatonin are produced in bright light, causing alertness.
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Which hormone is responsible for the development of male reproductive structures and male secondary sexual characteristics?
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Besides producing female sex cells (ova or eggs), OVARIES also produce two groups of steroid hormones, ______ & ______.
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Match the hormone with its function: Melatonin
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What is the primary function of parathyroid hormone (PTH)?
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Calcitonin is a hypercalcemic hormone.
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What causes progressive decalcification of bones associated with aging?
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Hypoparathyroidism can be caused by surgical removal of thyroid and parathyroid glands or injury to the glands, resulting in abnormally low levels of __________.
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Match the following hormones with their main functions:
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What is the major hormone produced by the Anterior Pituitary Gland?
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Which hormone is responsible for increasing protein synthesis and breakdown of fats and carbohydrates?
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Acromegaly occurs when Human Growth Hormone (HGH) is too high after childhood.
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Oxytocin causes milk ejection, also known as the __________ reflex.
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Match the following hormones with their glandular origin:
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Study Notes
Endocrine System Overview
- The endocrine system, along with the nervous system, helps maintain homeostasis in the body.
- The endocrine system uses chemical messengers called hormones to stimulate muscles and glands into action, whereas the nervous system uses impulses.
- Response to endocrine system stimulation is slower compared to the nervous system.
Functions of the Endocrine System
- Controls homeostasis
- Maintains water balance
- Controls uterine contractions
- Regulates milk production
- Regulates metabolism and growth
- Regulates heart rate and blood pressure
- Monitors blood glucose levels
- Aids the immune system
- Regulates reproductive functions
Components of the Endocrine System
- Ductless glands that secrete their products directly into the bloodstream
- Examples: pituitary gland, thyroid gland, adrenal glands, pancreatic islets, gonads
Types of Chemical Signals
- Intracellular: released within a cell and affects another part of the same cell
- Intercellular: released from one cell and binds to receptors on another cell
- Autocrine: released by cells and has a local effect on the same cell type
- Paracrine: released by cells and affects other cell types in close proximity
Hormones
- Chemical substances secreted by endocrine cells into the extracellular fluid that regulate the metabolic activity of other cells
- Types:
- Amino acid-based (amine)
- Protein-based (polypeptide)
- Steroid-based (lipid-soluble)
Mechanism of Hormone Action
- Direct gene activation: used by steroid hormones, which diffuse through the plasma membrane and bind to receptors in the nucleus
- Second-messenger system: used by water-soluble hormones, which bind to receptors on the plasma membrane and trigger a cascade of reactions
Control of Hormone Release
- Negative feedback mechanism: hormonal secretion is triggered by internal or external stimuli, then inhibited by rising hormonal levels
- Hormonal stimuli: most common stimulus, where endocrine organs are triggered into action by other hormones
- Humoral stimuli: changing blood levels of ions and nutrients stimulate hormone release
- Neural stimuli: nerve fibers stimulate hormone release and target cells respond to neural stimuli
Endocrine Glands
- Pituitary gland: divided into anterior and posterior regions, produces 7 hormones that regulate growth and development
- Thyroid gland: produces thyroid hormones that regulate metabolism
- Adrenal gland: produces hormones that regulate stress response and electrolyte balance
- Parathyroid gland: produces hormone that regulates calcium levels
- Pineal gland: produces hormone that regulates sleep-wake cycle
- Thymus: produces hormone that regulates immune system development
- Pancreas: produces hormones that regulate blood sugar levels
- Gonads (ovaries and testes): produce sex hormones that regulate reproductive functions### Thyroid Gland
- Acts as a storage area for hormones produced by hypothalamic neurons
- Produces two main hormones: Thyroxine (T4) and Triiodothyronine (T3)
- T4 and T3 regulate metabolism of carbohydrates, fats, and proteins
- Necessary for normal tissue growth and development, especially in reproductive and nervous systems
- Target tissues: almost all tissues
Disorders of Thyroid Gland
- Hypothyroidism: lack or low level of thyroid hormone
- Symptoms: decreased metabolism, weight gain, reduced appetite, fatigue, sluggishness, dry skin, and low temperature
- Hyperthyroidism: too much secretion of thyroid hormone
- Symptoms: increased metabolism, weight loss, increased appetite, nervousness, higher temperature, and warm skin
- Graves' disease: associated with enlarged thyroid gland or goiter and bulging of eyeballs
Parathyroid Gland
- Four glands located on the posterior surface of the thyroid gland
- Produces Parathyroid Hormone (PTH) which regulates calcium ion (Ca2+) homeostasis in the blood
- PTH stimulates bone destruction cells to break down bone matrix and release Ca into the blood
- Target tissues: skeleton, kidneys, and intestine
Disorders of Parathyroid Gland
- Hypoparathyroidism: abnormally low level of PTH
- Symptoms: decreased Ca levels in blood, tetany, and muscle cramps
- Hyperparathyroidism: abnormally high level of PTH
- Symptoms: increased Ca levels in blood, bone matrix breakdown, and muscle weakness
Adrenal Gland
- Two bean-shaped glands located on top of the kidneys
- Structurally and functionally two endocrine organs in one: adrenal cortex and adrenal medulla
- Adrenal cortex produces three layers of hormones: Mineralocorticoids, Glucocorticoids, and Sex Hormones
- Adrenal medulla produces Epinephrine and Norepinephrine
Hormones of Adrenal Cortex
- Mineralocorticoids (Aldosterone)
- Regulate concentration of mineral electrolytes
- Regulate sodium reabsorption and potassium excretion by the kidneys
- Glucocorticoids (Cortisol and Cortisone)
- Promote normal cell metabolism and help the body resist long-term stressors
- Increase blood glucose levels and break down protein and fat for energy
- Sex Hormones (Androgen and Estrogen)
- Produced in small amounts in both males and females
- Stimulate development of male sexual characteristics
Disorders of Adrenal Gland
- Addison's disease: hyposecretion of the adrenal cortex
- Symptoms: peculiar bronze skin, muscle weakness, and hypoglycemia
- Hyperaldosteronism: excessive water and sodium retention, leading to high blood pressure and edema
- Cushing's syndrome: excessive glucocorticoid production
- Symptoms: "moon face", buffalo hump, hypertension, and hyperglycemia
- Hypersecretion of Sex Hormones
- Leads to masculinization, facial hair growth, and deep voice
Pancreas
- Dual role: part of the digestive system and part of the endocrine system
- Produces digestive enzymes and two main hormones: Insulin and Glucagon
- Insulin and Glucagon regulate blood glucose levels
Disorders of Pancreatic Islets
- Diabetes Mellitus: too little insulin or faulty insulin receptors
- Symptoms: polyphagia, polyuria, dehydration, and fatigue
- Diabetes Ketoacidosis (DKA)
- When large amounts of fats are used for energy, blood becomes acidic, and ketones appear in the blood
Thymus
- Produces hormone Thymosin which causes production of T lymphocytes
- T lymphocytes protect the body against foreign microorganisms
Pineal Gland
- Produces hormone Melatonin which regulates sleep-wake cycles
Gonads
- Female and male gonads produce sex hormones identical to those produced by the adrenal cortex
- Testes produce testosterone, the principal male sex hormone responsible for the development of male reproductive structures and enlargement of penis and testes.### Testosterone
- Promotes male secondary sexual characteristics, including growth of facial and chest hair, deepening of the voice, muscular development, and bone growth.
- Stimulates the development of male sexual drive and aggressiveness.
- Production is stimulated by LH from the APG.
Melatonin
- Inhibits secretion of gonadotropin hormones from the APG, coordinating the hormones of fertility.
- Believed to be the "sleep trigger" that plays an important role in establishing the body's day-night cycle (circadian rhythm).
- Bright light inhibits secretion, making people feel good, while high levels are produced in the dark, causing individuals to feel depressed, tired, and fall asleep.
- Plays a role in the onset of puberty and in the female reproductive cycle.
Ovaries
- Paired, almond-sized organs located in the pelvic cavity.
- Produce female sex cells (ova or eggs) and two groups of steroid hormones: estrogen and progesterone.
Estrogen
- Responsible for the development of sex characteristics in women, including growth and maturation of reproductive organs.
- Promotes the appearance of secondary sexual characteristics, such as hair in pubic and axillary regions, breast development, fat deposition on hips and thighs, and bone development resulting in broad hips and high-pitched voice.
Estrogen and Progesterone
- Together, they promote breast development and cyclic changes in uterine lining (menstrual cycle).
Progesterone
- Acts with estrogen to bring about the menstrual cycle.
- During pregnancy, it relaxes uterine muscles and prepares the breast for lactation.
Thymus Gland
- Located at the upper thorax, posterior to the sternum.
- Large in infants and children, decreasing in size throughout adulthood.
- Critical in the development of the immune system.
Hypothalamus and APG
- Releasing hormones from the hypothalamus affect the APG to produce gonad-stimulating hormones (FSH and LH).
- FSH and LH from the APG stimulate the ovaries to produce hormones estrogen and progesterone.
Serotonin
- Secreted by the pineal gland, acts as a neurotransmitter and vasoconstrictor.
- Stimulates smooth muscle contraction and inhibits gastric secretions.
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Description
An introduction to the endocrine system, including its role in maintaining homeostasis and how it works with the nervous system. Learn about paracrine and neurotransmitters.
