Chapter 16 – The Endocrine System
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Transcript of Chapter 16 – The Endocrine System
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Chapter 16 – The Endocrine System
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Endocrine system
• Along with the nervous system, is responsible for homeostasis – Nervous system – fast-acting; short-term effects– Endocrine system – slow-acting; long-term effects
• Utilizes chemical messengers called hormones• Gland types – Exocrine – have ducts – Endocrine – ductless when mature
• Secrete into surrounding fluid and then enters bloodstream • Carried body-wide; affects distant tissues
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Endocrine System
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Structural classification of hormones
• Amino acid derivatives– Hydrophilic
• Peptide – Hydrophilic
• Lipid derivatives– Hydrophobic– Steroids; sex hormones – Synthesized from cholesterol
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Hydrophilic hormone receptors • Water soluble hormones can no
diffuse through plasma membrane; receptors are on cell surface – Transmembrane proteins – span
entire membrane • Hormone binds to receptor;
receptor changes shape • Shape change activates G protein
– Converts to an active form – Starts chain reaction that ultimately
activates kinases • Kinases attach phosphate groups to
molecules – This either activates the molecule or
inactivates it, depending on the specific molecule
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Hydrophobic hormone receptors • Fat soluble
hormones can diffuse through plasma membrane – Receptors are
located in cell’s interior (the cytoplasm)
• Hormone-receptor complex enters nucleus and binds to DNA to affect gene expression
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Control of hormone release
• Endocrine reflexes – Humoral • Detects and responds to change in concentration of
certain molecules – Neural • Signal from nervous system stimulates secretion
– Hormonal • Some hormones target other endocrine glands
– Tropic hormones (sometimes called trophic hormones)
• All can be modified by nervous system
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Pituitary gland (hypophysis)
• Located in the sella turcica of the sphenoid bone
• Attached to the hypothalamus by a stalk called the infundibulum
• 2 lobes – Posterior
(neurohypophysis)– Anterior
(adenohypophysis)
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Pituitary gland hormones
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Posterior pituitary (neurohypophysis)
• Composed of neural tissue; stores and releases hormones produced by the hypothalamus
• Antidiuretic hormone (ADH)– Increases water reabsorption
• Aquaporins placed in the collecting ducts of the kidneys • Increases blood volume/pressure
• Oxytocin (OXT)– Stimulates smooth muscle contractions
• Uterine contractions during childbirth• Milk letdown in lactating females • Durng sexual arousal in males and females
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Anterior pituitary (adenohypophysis)
• Release or inhibition is controlled by hypothalamus
• Growth hormone (GH)– Bones and skeletal muscles the major target
tissues • Melanocyte-stimulating hormone (MSH)– Stimulates melanocytes in skin; contributes to skin
pigmentation
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Anterior pituitary (adenohypophysis)
• Tropic hormones – Thyroid-stimulating hormone (TSH)• Thyroid gland
– Adrenocorticotropic hormone (ACTH)• Adrenal cortex
– Follicle-stimulating hormone (FSH)• Gonads to produce gametes
– Leutinizing hormone (LH)• Stimulation of gonadal hormones
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Thyroid gland
• On trachea, inferior to larynx
• Butterfly-shaped – 2 lobes
connected by isthmus
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Thyroid gland microscopic anatomy • Follicle cells produce
thyroglobin (a glycoprotein) – Simple cuboidal epithelium – Central cavity of follicles is
filled with colloid – thyroglobulin with iodine atoms • Forms T3 and T3 hormones
• Parathyroid cells (C cells) produce calcitonin
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Thyroid hormones
• Thyroxine (T4) and Triiodothyronine (T3)– #4 and #3 refer to number of iodine atoms attached – Affects most cell in body• Increases basal metabolic rate and heat production • Aids in maintenance of blood pressure • Helps regulate growth and development
• Calcitonin – Lowers blood calcium levels • Inhibits osteoclasts
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Parathyroid glands • Usually 4 on posterior
thryoid • Parathyroid hormone– Produced by chief cells – Increases blood calcium levels
• Antagonistic to calcitonin • Stimulates osteoclasts• Increases reabsorption of
calcium by kidneys – Kidney also converts vitamin D
to its active form, which aids in calcium absorption in digestive system
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Adrenal glands
• Also called suprarenal glands due to their location
• Adrenal cortex (superficial) and adrenal medulla (deep)
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Adrenal cortex microscopic anatomy
• 3 layers/zones (superficial to deep)– Zona glomerulosa
• Produces mineralcorticoids – Zona fasciculata
• Produces mainly glucocorticoids, some gonadocorticoids
– Zona reticularis • Produces mainly
gonadocortcoids, some glucocorticoids
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Adrenal cortex hormones • Mineralcorticoids
– Regulation of electrolytes in extracellular fluid– Aldosterone
• Stimulates sodium reabsorption in distal convoluted tubules of kidneys
• Glucocorticoids – Influence energy metabolism – Regulates blood glucose and blood pressure levels – Cortisol (hydrocortisone)
• Gluconeogenesis – formation of glucose from non-carbohydrate sources – Excess of glucocorticoids results in oversuppression of inflammatory and anti-
immune responses • Gonadocorticoids
– Androgens• Male sex hormones • Converted to testosterone in males; estrogen in females
– Estrogens
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Adrenal medulla hormones
• Autonomic nervous system• Epinephrine and norepinephrine – “Fight or flight” response – Blood glucose levels rise, increases heart rate,
blood directed to cardiac and skeletal muscles – Epinephrine serves as a blood vessel contrictor
and a bronchiole dilator
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Pineal gland
• Located at roof of third ventricle in brain
• Melatonin – Concentration rises
and falls within a 24 hour time period • Peaks at night – causes
sleepiness – Affects biological
clock/circadian rhythms
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Pancreas• Posterior to stomach • Microscopic anatomy– Acinar cells
• Produce pancreatic secretions for digestive system
– Islets of Langerhans• Alpha cells – produce
glucagon • Beta cells – produce
insulin
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Pancreatic hormones• Glucagon – Increases blood glucose levels
• Glycogenolysis – Breaks down glycogen to glucose
• Gluconeogenesis – Synthesizes glucose from non-carbohydrate sources
• Releases glucose from the liver
• Insulin – Decreases blood glucose levels (antagonistic to glucagon)
• Increases glucose transport into cells (primarily adipose and muscle)– Uses glucose for ATP production – Stores as glycogen – Excess stored as fat
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Thymus
• Overlays heart • Produces several
peptide hormones – Thymosin, thymopoetin,
thymic factor – Development/maturation
of T lymphocytes
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Gonadal hormones • Hormones are steroids (fat-soluble)• Ovaries (female)– Estrogen
• Secondary sex characteristics • Maturation of reproductive organs
– Progesterone • Along with estrogen:
– Breast development and menstrual cycle regulation
• Testes (male)– Testosterone
• Secondary sex characteristics • Maturation of reproductive organs • Production of sperm