Hormones and the Endocrine System

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Hormones and the Endocrine System

• Chapter 45

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Hormones

• The Bodys Long-Distance Regulators
• Chemical signals secreted into the circulatory
  system that communicate regulatory messages
  within the body
• Hormones may reach all parts of the body
• But only certain types of cells, target cells,
  are equipped to respond

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Endocrine system and the Nervous system

• The two systems animals have of internal
  communication and regulation
• The nervous system
• Conveys high-speed electrical signals along
  specialized cells called neurons
• The endocrine system
• made up of endocrine glands
• Secretes hormones that coordinate slower but
  longer-acting responses to stimuli
• The two systems often function together in
  maintaining homeostasis, development, and
  reproduction

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Control Pathways and Feedback Loops

• There are three types of hormonal control
  pathways
• Simple endocrine pathway
• Simple neurohormone pathway
• Simple neuroendocrine pathway

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Hormones and Cell Responses

• Hormones convey information via the blood stream
  to target cells throughout the body
• Three major classes of molecules function as
  hormones in vertebrates
• Proteins and peptides
• Amines derived from amino acids
• Steroids
• Signaling by any of these molecules involves
  three key events
• Reception
• Signal transduction
• Response

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Cell-Surface Receptors

• The receptors for most water-soluble hormones
• Are embedded in the plasma membrane, projecting
  outward from the cell surface
• Binding of a hormone to its receptor
• Initiates a signal transduction pathway leading
  to specific responses in the cytoplasm or a
  change in gene expression

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Different Effects of the Same Hormone

• The same hormone may have different effects on
  target cells that have
• Different receptors for the hormone
• Different signal transduction pathways
• Different proteins for carrying out the response

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Hormone- Epinephrine
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Intracellular Receptors

• Lipid-Soluble Hormones
• Steroids, thyroid hormones, and the hormonal form
  of vitamin D
• Enter target cells and bind to specific protein
  receptors in the cytoplasm or nucleus
• The protein-receptor complexes
• Then act as transcription factors in the nucleus,
  regulating transcription of specific genes

(b) Receptor in cell nucleus
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Local Regulators? Paracrine Signaling

• Various types of chemical signals elicit
  responses in nearby target cells
• Local regulators have various functions and
  include
• Neurotransmitters
• Cytokines and growth factors
• Nitric oxide
• Prostaglandins

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The major human endocrine glands

• Tropic hormonestarget other endocrine glands and
  are important tounderstanding chemical
  coordination.
• Humans havenine endocrineglands.
• The hypothalamus and the pituitary gland
• Control much of the endocrine system

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Relation Between the Hypothalamus and Pituitary
Gland

• The hypothalamus integrates endocrine and nervous
  function.
• Neurosecretory cells of the hypothalamus produce
  hormones.
• Releasing hormones stimulate the anterior
  pituitary (adenohypophysis) to secrete hormones.
• Inhibiting hormones prevent the anterior
  pituitary from secreting hormones.

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The posterior pituitary (neurohypo-physis)

• Stores andsecretes hormonesproducedby
  thehypothalamus

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Hormones manufactured by the hypothalamus and
released by the posterior pituitary

• Oxytocin a peptide.
• Stimulates contraction of the uterus and mammary
  glands.
• Secretion regulated by the nervous system.
• Antidiuretic hormone (ADH) a peptide.
• Promotes retention of water by the kidneys.
• Secretion regulated by water/salt balance.

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Anterior Pituitary Hormones
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Anterior Pituitary Hormones

• Growth hormone (GH) a protein.
• Stimulates growth and metabolism.
• Secretion regulated by hypothalamic hormones.
• Acts directly on tissues or acts via growth
  factors.
• Gigantism excessive GH during development.
• Acromegaly excessive GH production during
  adulthood.
• Hypopituitary dwarfism childhood GH deficiency

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Anterior Pituitary Hormones(Tropic)

• Gonadotropins glyocoproteins.
• Follicle-stimulating hormone (FSH).
• Stimulates production of sperm and ova.
• Secretion regulated by hypothalamic hormones.
• Luteinizing hormone (LH).
• Stimulates ovaries and testes.
• Secretion regulated by hypothalamic hormones.

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Anterior Pituitary Hormones(Tropic)

• Thyroid-stimulating hormone (TSH) a
  glycoprotein.
• Stimulates thyroid gland.
• Secretion regulated by thyroxine in blood.
• Secretion regulated by hypothalamic hormones.
• Adrenocorticotropic hormone (ACTH) a peptide
• Stimulates adrenal cortex secretion of
  glucocorticoids
• Secretion regulated by glucocorticoids and
  hypothalamic hormone

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Anterior Pituitary Hormones(Nontropic)

• Prolactin (PRL) a protein.
• Stimulates milk production and secretion.
• Secretion regulated by hypothalamic hormones.
• Melanocyte-stimulating hormone (MSH) a peptide.
• May play a role in fat metabolism.
• Endorphins peptides.
• Inhibit pain perception.
• Effects mimicked by heroin and other opiate drugs.

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Nonpituitary hormones help regulate metabolism,
homeostasis, development, and behavior

• Regulate various functions in the body

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The hypothalamus and anterior pituitary

• Control the secretion of thyroid hormones through
  two negative feedback loops

Figure 45.9
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Thyroid Hormones

• The thyroid gland
• Consists of two lobes located on the ventral
  surface of the trachea
• Produces two iodine-containing hormones,
  triiodothyronine (T3) and thyroxine (T4) The
  thyroid hormones
• Play crucial roles in stimulating metabolism and
  influencing development and maturation

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Hyperthyroidism, excessive secretion of thyroid
hormones

• Can cause Graves disease in humans

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Calcitonin?Calcium Homeostasis
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Insulin and Glucagon
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Diabetes Mellitus

• Diabetes mellitus, perhaps the best-known
  endocrine disorder
• Is caused by a deficiency of insulin or a
  decreased response to insulin in target tissues
• Is marked by elevated blood glucose levels

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• Type I diabetes mellitus (insulin-dependent
  diabetes)
• Is an autoimmune disorder in which the immune
  system destroys the beta cells of the pancreas
• Type II diabetes mellitus (non-insulin-dependent
  diabetes)
• Is characterized either by a deficiency of
  insulin or, more commonly, by reduced
  responsiveness of target cells due to some change
  in insulin receptors

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Adrenal Hormones Response to Stress

• The adrenal glands
• Are adjacent to the kidneys
• Are actually made up of two glands the adrenal
  medulla and the adrenal cortex

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Catecholamines from the Adrenal Medulla

• The adrenal medulla secretes epinephrine and
  norepinephrine
• Hormones which are members of a class of
  compounds called catecholamine
• These hormones
• Are secreted in response to stress-activated
  impulses from the nervous system
• Mediate various fight-or-flight responses

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Stress Hormones from the Adrenal Cortex

• Function in the bodys response to stress
• Fall into three classes of steroid hormones
• Glucocorticoids, such as cortisol
• Influence glucose metabolism and the immune
  system
• Mineralocorticoids, such as aldosterone
• Affect salt and water balance
• Sex hormones
• Are produced in small amounts

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• Stress and the adrenal gland

Stress
Nerve signals
Hypothalamus
Spinal cord (cross section)
Releasing hormone
Nerve cell
Anterior pituitary
Blood vessel
Adrenal medulla secretes epinephrine and
norepinephrine.
Nerve cell
Adrenal cortex secretes mineralocorticoids and
glucocorticoids.
ACTH
Adrenal gland
Kidney
(a) Short-term stress response
(b) Long-term stress response
Effects of epinephrine and norepinephrine
Effects of mineralocorticoids
Effects of glucocorticoids
1. Glycogen broken down to glucose
increasedblood glucose
1. Retention of sodiumions and water bykidneys
1. Proteins and fatsbroken down andconverted to
glucose,leading to increasedblood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
2. Increased bloodvolume and bloodpressure
5. Change in blood flow patterns, leading to
increased alertness and decreased digestive
and kidney activity
2. Immune system may be suppressed
Figure 45.13a,b
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Gonadal Sex Hormones

• The gonadstestes and ovaries
• produce most of the bodys sex hormones
  androgens, estrogens, and progestins
• The testes primarily synthesize androgens, the
  main one being testosterone
• Which stimulate the development and maintenance
  of the male reproductive system

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Testosterone causes an increase in muscle and
bone mass

• Is often taken as a supplement to cause muscle
  growth, which carries many health risks

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Estrogen And Progesterone

• Estradiol ? most important of Estrogens
• Responsible for the maintenance of the female
  reproductive system and the development of female
  secondary sex characteristics
• Progestins? progesterone
• Primarily involved in preparing and maintaining
  the uterus?supports growth and development of the
  embryo

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Melatonin and Biorhythms

• The pineal gland is a small mass of tissue near
  the center of the mammalian brain
• Secretes the hormone, melatonin, an amine.
• Involved in biological rhythms associated with
  reproduction.
• Secretion regulated by light/dark cycles