Chapter 16 the endocrine system
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Chapter 16 – The Endocrine System . 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

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Chapter 16 – The Endocrine System

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Chapter 16 the endocrine system

Chapter 16 – The Endocrine System


Endocrine system

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


Endocrine system1

Endocrine System


Structural classification of hormones

Structural classification of hormones

  • Amino acid derivatives

    • Hydrophilic

  • Peptide

    • Hydrophilic

  • Lipid derivatives

    • Hydrophobic

    • Steroids; sex hormones

    • Synthesized from cholesterol


Hydrophilic hormone receptors

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


Hydrophobic hormone receptors

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


Control of hormone release

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


Pituitary gland hypophysis

Pituitary gland (hypophysis)

  • Located in the sellaturcica of the sphenoid bone

  • Attached to the hypothalamus by a stalk called the infundibulum

  • 2 lobes

    • Posterior (neurohypophysis)

    • Anterior (adenohypophysis)


Pituitary gland hormones

Pituitary gland hormones


Posterior pituitary neurohypophysis

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


Anterior pituitary adenohypophysis

Anterior pituitary (adenohypophysis)

  • Release or inhibition is controlled by hypothalamus

  • Growth hormone (GH)

    • Bones and skeletal muscles the major target tissues

  • Prolactin (PRL)

    • Stimulates milk production

  • Melanocyte-stimulating hormone (MSH)

    • Stimulates melanocytes in skin; contributes to skin pigmentation


Anterior pituitary adenohypophysis1

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


Thyroid gland

Thyroid gland

  • On trachea, inferior to larynx

  • Butterfly-shaped

    • 2 lobes connected by isthmus


Thyroid gland microscopic anatomy

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


Thyroid hormones

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


Parathyroid glands

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


Adrenal glands

Adrenal glands

  • Also called suprarenal glands due to their location

  • Adrenal cortex (superficial) and adrenal medulla (deep)


Adrenal cortex microscopic anatomy

Adrenal cortex microscopic anatomy

  • 3 layers/zones (superficial to deep)

    • Zonaglomerulosa

      • Produces mineralcorticoids

    • Zonafasciculata

      • Produces mainly glucocorticoids, some gonadocorticoids

    • Zonareticularis

      • Produces mainly gonadocortcoids, some glucocorticoids


Adrenal cortex hormones

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


Adrenal medulla hormones

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


Pineal gland

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


Pancreas

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


Pancreatic hormones

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


Thymus

Thymus

  • Overlays heart

  • Produces several peptide hormones

    • Thymosin, thymopoetin, thymic factor

    • Development/maturation of T lymphocytes


Gonadal hormones

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


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