9.2: The Major Endocrine Organs

Transcription

1 9.2: The Major Endocrine Organs ANATOMY & PHYSIOLOGY

2 The Major Endocrine Organs Below is a list of the major endocrine organs that we will worry about for this class We will look at hormones associated with each as well as disorders that can arise from each Major organs include: Pituitary gland Thyroid gland Parathyroid gland Adrenal glands Pineal gland Thymus gland Pancreas Gonads (Ovaries and Testes) Hypothalamus Figure 9.3

3 Pituitary Gland Size of a pea Hangs by a stalk from the hypothalamus in the brain Protected by the sphenoid bone Two functional lobes Anterior pituitary glandular tissue Posterior pituitary nervous tissue Often called the master endocrine gland

4 Hormones Associated with Anterior Lobe of Pituitary (ALP) Characteristics of all anterior pituitary hormones Protein based Act through second-messenger systems Regulated by hormonal stimuli, mostly negative feedback Six hormones associated: Two with nonendocrine targets Growth hormone (GH) Prolactin (PRL) Four stimulate other endocrine glands Thyroid-stimulating hormone (thyrotropic hormone) (TH) Adrenocorticotropic hormone (ACTH) Two gonadotropic hormones Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Figure 9.4

5 Hormones of the ALP (Growth Hormone) General metabolic hormone Major effects are directed to growth of skeletal muscles and long bones Plays a role in determining final body size Causes amino acids to be built into proteins Causes fats to be broken down for a source of energy

6 Growth Hormone (GH) Disorders Pituitary dwarfism Hyposecretion of GH during childhood Gigantism Hypersecretion of GH during childhood Acromegaly Hypersecretion of GH during adulthood Figure 9.5

7 Hormones of the ALP Prolactin (PRL) Stimulates and maintains milk production following childbirth Function in men is unknown Adrenocorticotropic hormone (ACTH) Regulates the endocrine activity of the cortex portion of the adrenal glands Thyroid-stimulating hormone (TSH) Also known as the thyrotropic hormone (TH) Influences the growth and activity of the thyroid gland

8 Hormones of the ALP Gonadotropic hormones Regulate the hormonal activity of the gonads (ovaries and testes) Two types Follicle-stimulating hormone (FSH) In women, stimulates follicle development in the ovaries As the follicles mature, they produce estrogen and eggs are readied for ovulation In men, stimulates sperm development by the testes Luteinizing hormone (LH) In women, triggers ovulation of an egg from the ovary Causes the ruptured follicle to produce progesterone and some estrogen In men, stimulates testosterone production by the interstitial cells of the testes

9 Pituitary-Hypothalamus Relationship Hormonal release is regulated by releasing and inhibiting hormones produced by the hypothalamus Hypothalamus produced two hormones Oxytocin Antidiuretic hormone These are transported to neurosecretory cells of the posterior pituitary The posterior pituitary is not strictly an endocrine gland, but does release hormones

10 Hormones of the Posterior Pituitary Gland (PPL) Oxytocin Released in significant amounts only during childbirth and in nursing women Stimulates contractions of the uterus curing labor, during sexual relations, and during breastfeeding Also causes milk ejection in a nursing women Figure 9.6

11 Hormones of the PPL (cont.) Antidiuretic hormone (ADH) RECALL: diuresis is urine production Inhibits urine production by promoting water reabsorption by the kidneys In large amounts, causes vasoconstriction leading to increased blood pressure Can be inhibited by drinking alcoholic beverages Hyposecretion of ADH leads to excessive urine output called diabetes insipidus Continually thirsty and drink huge amounts of water Figure 9.6

12 Thyroid Gland Found at the base of the throat Consists of two lobes and a connecting isthmus Produces two hormones Thyroid hormone Calcitonin Figure 9.7

13 Hormones Associated with the Thyroid Gland Thyroid hormone Major metabolic hormone Composed of two active iodine-containing hormones Thyroxine (T 4 ) secreted by thyroid follicles Triiodothyronine (T 3 ) conversion of T 4 at target tissues Controls the rate at which glucose is burned or oxidized Also important for normal tissue growth and development, especially in the reproductive and nervous systems

14 Thyroid Hormone Disorders Goiters Enlarged thyroid gland due to lack of iodine Salt is iodized to prevent goiters Cretinism Caused by hyposecretion of thyroxine Results in dwarfism during childhood Figure 9.8

15 Thyroid Hormones Disorders (cont.) Myxedema Hypothyroidism in adults Results in physical and mental sluggishness (but no mental retardation) Graves disease Caused by hyperthyroidism Increased metabolism, heat intolerance, rapid heartbeat, weight loss, and exophthalmos Figure 9.9

16 Hormones Associated with the Thyroid Gland Calcitonin Decreases blood calcium levels by causing its deposition on bone Antagonistic to parathyroid hormone Produced by parafollicular cells Parafollicular cells are found between the follicles Few effects of hypo- or hypersecretion of calcitonin are known, and calcitonin production is meager or ceases entirely in adults May help to explain (at least in part) the progressive decalcification of bones that accompanies aging

17 Parathyroid Glands Tiny masses on the posterior of the thyroid Secrete the parathyroid hormone (PTH) Most important regulator of calcium ion (Ca 2+ ) homeostasis of the blood Mechanism can be seen in Figure 9.10 Low blood calcium levels can result in tetany (uncontrollable muscle spasms) Severe hyperparathyroidism causes massive bone destruction Figure 9.10

18 Adrenal Glands Sit on top of the kidneys Two regions Adrenal cortex outer glandular region with three layers Mineralocorticoids secreted by outermost layer Glucocorticoids secreted by middle layer Sex hormones secreted by innermost layer Adrenal medulla inner neural tissue region Figure 9.11

19 Hormones of the Adrenal Cortex Mineralocorticoids (mainly aldosterone) Produced in outer adrenal cortex Regulate mineral content in the blood Regulate water and electrolyte balance Target organ is kidneys Production stimulated by humoral factors (as seen in Figure 9.12) Production inhibited by atrial natriuretic peptide (ANP) Figure 9.12

20 Hormones of the Adrenal Cortex (cont.) Glucocorticoids (include cortisone and cortisol) Produced in middle layer of adrenal cortex Promote normal cell metabolism Help resist long-term stressors Released in response to increased blood levels of ACTH Figure 9.13 shows the mechanism for the long-term stress response handled by the adrenal cortex

21 Figure 9.13

22 Hormones of the Adrenal Cortex (cont.) Sex hormones Produced by the inner layer of the adrenal cortex Small amounts are made throughout life Mostly androgens (male sex hormones) are made but some estrogens (female sex hormones) are also formed

23 Adrenal Cortex Disorders Addison s disease Hyposecretion of all adrenal cortex hormones Bronze skin tone, muscles are weak, burnout, susceptible to infection Hyperaldosteronism May result from an ACTH-releasing tumor Excess water and sodium are retained leading to high blood pressure and edema Cushing s Syndrome Results from a tumor in the middle cortical area of the adrenal cortex Moon face, buffalo hump on the upper back, high blood pressure, hyperglycemia, weakening of the bones, depression Masculinization Results from hypersecretion of sex hormones Beard and male distribution of hair growth

24 Hormones of the Adrenal Medulla Produces two similar hormones (catecholamines) Epinephrine (adrenaline) Norepinephrine (noradrenaline) Prepare body for short-term stress ( fight or flight ) Mechanism can be seen on Figure 9.13 Figure 9.11

25 Figure 9.13 (again)

26 Pancreatic Islets The pancreas is a mixed gland and has both endocrine and exocrine functions The pancreatic islets produce the following hormones: Insulin allows glucose to cross plasma membranes into cells Glucagon allows glucose to enter the blood Both of these help maintain blood sugar homeostasis (Figure 9.15)

27 Figure 9.15

28 Pancreatic Islets Disorders Hyposecretion of insulin plays a role in maintaining blood levels of glucose Without insulin, glucose levels rise from normal range (between 80 to 120 mg/100 ml of blood) to high levels (i.e. 600 mg/100 ml of blood) Disorder is known as diabetes mellitus

29 Pineal Gland Found on the third ventricle of the brain Secretes melatonin Helps establish the body s wake and sleep cycles Believed to coordinate the hormones of fertility in humans Figure 9.3

30 Thymus Gland Located posterior to the sternum Largest in infants and children Produces thymosin Matures some types of white blood cells Important in developing the immune system Figure 9.3

31 Gonads Ovaries Produce eggs Produce two groups of steroid hormone Estrogens Progesterone Testes Produce sperm Produce androgens, such as testosterone Figure 9.3

32 Hormones of the Ovaries Estrogens Stimulate the development of secondary female characteristics Mature female reproductive organs With progesterone, estrogens also Promote breast development Regulate menstrual cycle Progesterone Acts with estrogen to bring about the menstrual cycle Helps in the implantation of an embryo in the uterus Helps prepare breasts for lactation

33 Hormones of the Testes Produce several androgens Testosterone is the most important Responsible for adult male secondary sex characteristics Promotes growth and maturation of male reproductive system Required for sperm cell production

34 For Next Time Reading: pg Homework: 9.2 Worksheets (4-9)