Chapter 16 Endocrine System Flashcards
The body’s second great controlling system which influences metabolic activities of cells by means of hormones is
the endocrine system
Endocrine glands are
the pituitary, thyroid, parathyroid, adrenal, pineal, and thymus
The pancreas and gonads produce both
hormones and exocrine products
What has both neural functions and releases hormones?
the hypothalamus
Other tissues and organs that produce hormones are:
adipose cells, pockets of cells in the walls of the small intestine, stomach, kidneys, and heart
Major endocrine organs
Autocrines
chemicals that exert effects on the same cells that secrete them
Paracrines
locally acting chemicals that affect cells other than those that secrete them
Autocrines and Paracrines are
not considered hormones since hormones are long-distance chemical signals
Hormones
chemical substances secreted by cells into the extracellular fluids
- regulate the metabolic function of other cells
- have lag times ranging from seconds to hours
- tend to have prolonged effects
- are classified as amino acid-based hormones or steroids
Elcosanoids
biologically active lipids with local hormone-like activity
Types of hormones
-
amino acid-based
- amines, thyroxine, peptide and protein hormones
- Steroids-gonadal and adrenocortical hormones
- Elcosanoids-leukotrienes and prostaglandins
Hormones alter target cell activity by one of two mechanisms
-
second messengers:
- regulatory G proteins
- amino acid-based hormones
-
direct gene activation
- steroid hormones
The precise response depends on the type of target cell
Hormones produce one or more of the following cellular changes in target cells:
- alter plasma membrane permeability
- stimulate protein synthesis
- activate or deactivate enzyme systems
- induce secretory activity
- stimulate mitosis
Amino Acid-Based hormone action:
cAMP Second Messenger*
- hormone (first messenger) binds to its receptor, which then binds to a G protein
- the G protein is then activated as it binds GTP, displacing GDP
- activated G protein activated the effector enzyme adenylate cyclase
- adenylate cyclase generates cAMP (second messenger) from ATP
- cAMP activates protein kinases, which then cause cellular effects
Amino Acid-Based Hormone Action:
PIP-Calcium*
- hormone binds to the receptor and activates the G protein
- G protein binds and activates phospholipase
- phospholipase splits and phospholipids PIP2 into diacylglycerol (DAG) and IP3 (both act as second messengers
- DAG activates protein kinases; IP3 triggers the release of Ca2+ stores
- Ca2+ (third messenger) alters cellular responses
Steroid hormones
- this interaction prompts DNA transcription to produce mRNA
- the mRNA is translated into proteins, which bring about a cellular effect
Target Cell Specificity
- hormones circulate to all tissues but only activate cells referred to as target cells
- target cells must have specific receptors to which the hormone binds
- these receptors may be intracellular or located on the plasma membrane
Target cell Activation depends on three factors:
- Blood Levels of the hormone
- Relative number of receptors on the target cell
- the affinity of those receptors for the hormone-(means how likely they will bind)
Up-regulation is when
target cells form more receptors in response to the hormone
Down-regulation is when
target cells lose receptors in response to the hormone
Hormones circulate in the blood in what two forms:
free or bound
Hormones are removed from the blood by:
- degrading enzymes
- the kidneys
- liver enzyme systems
Interaction of Hormones at Target Cells
The three types of hormone interaction:
- permissiveness
- synergism
- antagonism
permissiveness is when
one hormone cannot exert its effects without another hormone being present
synergism is when
more than one hormone produces the same effects on a target cell
antagonism is when
one or more hormones opposes the action of another hormone
Blood levels of hormones are
controlled by negative feedback systems
Hormones are synthesized and released in response to:
- Humoral stimuli
- Neural stimuli
- Hormonal stimuli
Humoral stimuli:
secretion of hormones in direct response to changing blood levels of ions and nutrients
Example: concentration of calcium ions in the blood
- declining blood Ca2+ concentration stimulates the parathyroid gland to secrete PTH (parathyroid hormone)
- PTH causes Ca2+ concentrations to rise and the stimulus is removed
Neural stimuli:
nerve fibers stimulate hormone release
Hormonal stimuli:
release of hormones in response to hormones produced by other endocrine organs
Major endocrine organs: Pituitary (Hyopohysis)
What are the 3
- pituitary gland
- neurohypophysis (posterior lobe)
- adenohypophysis (anterior lobe)
Pituitary gland:
a two-lobed organ that secrets nine major hormones
Neurohypophysis:
posterior lobe (neural tissue) and the infundibulum
- receives, stores and releases hormones from the hypothalamus
Adenohypophysis:
anterior lobe made up of glandular tissue
- synthesizes and secretes a number of hormones
Major Endocrine Organs: Pituitary (Hypophysis)
The six hormones of the adenohypophysis:
- abbreviated as GH, TSH, ACTH, FSH, LH, and PRL
- regulate the activity of other endocrine glands
In addition, pro-opiomelanocortin (POMC):
- has been isolated from the pituitary
- is split into ACTH, opiates, and MSH
Activity of the Adenophypophysis
The hypothalamus sends a chemical stimulus to the anterior pituitary
- Releasing hormones to stimulate the synthesis and release of hormones
- inhibiting hormones shut off the synthesis and release of hormones
The tropic hormones that are release are:
- Thyroid-stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
Growth Hormone (GH)
- produced by somatotropic cells of the anterior lobe that:
- stimulate most cells, but target bone and skeletal muscle
- promote protein synthesis and encourage the use of fats for fuel
Metabolic action of growth hormone:
- GH stimulates the liver, skeletal muscle, bone, and cartilage to produce insulin-like growth factors
Metabolic Action of Growth Hormone (GH)
Thyroid-stimulating hormone (Thyrotropin)
- stimulates the normal development and secretory activity of the thyroid
Adrenocorticotropic Hormone (Corticotropin)
- stimulates the adrenal cortex to release corticosteroids
- internal and external factors such as fever, hypoglycemia, and stressors can trigger the release of CRH
Gonadotropins-follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
- regulate the function of the ovaries and testes
- FSH stimulates gamete (egg or sperm) production
Prolactin (PRL)
- in females, stimulates milk production by the breasts
The posterior pituitary and hypothalamic hormones
posterior pituitary made of:
axons of hypothalamic neurons, stores antidiuretic hormone (ADH0 and oxygen
- ADH and oxytocin are synthesized in the hypothalamus
- ADH influences water balance
- Oxytocin stimulates smooth muscle contraction in breasts and uterus
- both use PIP-calcium second-messenger mechanism
Oxytocin:
- Oxytocin is a strong stimulant of uterine contraction
- regulated by a positive feedback mechanism to oxytocin in the blood
- this leads to an increase in the intensity of uterine contractions, ending in birth
- oxytocin triggers milk ejection (“letdown” reflex) in women producing milk
Antidiuretic Hormone (ADH)
ADH helps to:
-
avoid dehydration or water overload
- prevents urine formation
- alcohol inhibits ADH release and causes copious urine output
Thyroid Gland is the
largest gland, located in the anterior of the neck, consists of two lateral lobes connected by a median tissue mass called the isthmus
Thyroid Gland
Thyroid hormone is a:
major metabolic hormone
-
consists of two related iodine-containing compounds
- T4-thyroxine: has two tyrosine molecules plus four bound iodine atoms
- T3-triiodothyronine: has two tyrosines with three bound iodine atoms
Effects of Thyroid Hormone
TH is concerned with:
- glucose oxidation
- increasing metabolic rate
- heat production
Effects of Thyroid Hormone
TH plays a role in:
- maintaining blood pressure
- regulating tissue growth
- developing skeletal and nervous systems
- maturation and reproductive capabilities
Calcitonin
- a peptide hormone produced by the parafollicular, or C, cells
- lowers blood calcium levels in children
- antagonist to parathyroid hormone (PTH)
- calcitonin targets the skeleton
- regulated by a humoral (calcium ion concentration in the blood) negative feedback mechanism
Parathyroid glands are
- tiny glands embedded in the posterior aspect of the thyroid
- cells are arranged in cords containing oxyphil and chief cells
- chief (principal) cells secrete PTH
- PTH (parathormone) regulates calcium balance in the blood
Parathyroid Glands
Effects of Parathyroid Hormone
PTH release increases Ca2+ in blood as it:
- stimulates osteoclasts to digest bone matrix
- enhances the reabsorption of Ca2+ and the secretion of phosphate by the kidneys
- increases absorption of Ca2+ by intestinal mucosal
Rising Ca2+ in the blood inhibits PTH release
Effects of Parathyroid Hormone
Adrenal (Suprarenal) Glands
Adrenal glands:
- are paired, pyramid-shaped organs atop the kidneys
Structurally and functionally, they are two glands in one
- Adrenal medulla-neural tissue that acts as part of the SNS
- Adrenal cortex-glandular tissue derived from embryonic mesoderm
Adrenal Cortex
- synthesizes and releases steroid hormones called corticosteroids
- different corticosteroids are produced in each of the three layers
- Zona glomerulosa-mineralocorticoids: regulate electrolytes in extracellular fluids. (most important to aldosterone)
- Zona fasciculata-glucocorticoids: help the body resist stress. (Chiefly cortisol)
- Zona reticularis-gonadocorticoids: most are androgens (male sex hormones), and the most important one is testosterone. (androgens contribute to the onset of puberty)
Adrenal Cortex
Adrenal Medulla
made up of chromaffin cells that secrete epinephrine and norepinephrine
Pancreas
- a triangular gland, which has both exocrine and endocrine cells, located behind the stomach
Pancreatic islets (islets of Langerhans)
produce hormones (endocrine products)
The islets contain two major cell types:
- Alpha (a) cells that produce glucagon
- Beta (B) cells that produce insulin
Glucagon
Its major target is the liver, where it promotes:
- Glycogenolysis-the breakdown of glycogen to glucose
- Gluconeogenesis-synthesis of glucose from the lactic acid and noncarbohydrates
- release of glucose to the blood from liver cells
Insulin
- lowers blood glucose levels
Diabetes Mellitus (DM)
- Results from hyposecretion or hypoactivity of insulin
- The three cardinal signs of DM are:
- Polyuria-huge urine output
- Polydipsia-excessive thirst
- Polyphagia-excessive hunger and food consumption
Gonads: Female
- Paired ovaries in the abdominopelvic cavity produce estrogens and progesterone
- They are responsible for:
- maturation of the reproductive organs
- the appearance of secondary sexual characteristics
- breast development and cyclic changes in the uterine mucosa
Gonads: Male
- Testes located in an extra-abdominal sac (scrotum) produce testosterone
- Testosterone:
- initiates maturation of male reproductive organs
- causes the appearance of secondary sexual characteristics and sex drive
- is necessary for sperm production
- maintains sex organs in their functional state
Pineal Gland is the:
- small gland hanging from the roof of the third ventricle of the brain
- secretory product us melatonin
- melatonin is involved with:
- day/night cycles
Thymus
- lobulated gland located deep to the sternum
- these hormones are essential for the development of the T lymphocytes (T cells) of the immune system
- the thymus gland, located behind your sternum and between your lungs, is only active until puberty. After puberty, the thymus starts to slowly shrink and become replaced by fat.
