Download Wk 7. Assessment of the Endocrine and Metabolic System

Wk 7. Assessment of the Endocrine and Metabolic System
Metabolism: entire collection of chemical reactions that occur in all living cells
Metabolic processes
affect all cells of the body, whole-body metabolic regulation
involves numerous endocrine structures, the liver, muscle, fat, and brain cells
1. Structure of the metabolic systems
1) Endocrine system
Classification of hormones
- Steroids - Peptides: - Amino acid derivatives
(1) Hypothalamus and Pituitary Gland
pituitary gland (hypophysis): small (1 g) extension on dorsal surface of the hypothalamus
(2) Thyroid and Parathyroid
- Thyroid
located in the neck, just below cricoid cartilage
- Parathyroid glands
four small glands embedded in thyroid gland
(3) Endocrine Pancreas
Contain islets of Langerhans: secrete three hormones
alpha cells: secrete glucagons
beta cells: secrete insulin
delta cells secrete somatostatin (growth hormone inhibitory hormone) secreted by hypothalamus
(4) Adrenal Glands
Outer cortex and inner medulla
2. Function of the metabolic systems
Regulation of endocrine secretions: by negative feedback loop
linking hormone to a response, to another hormone, to glucose or someother plasma compound
1) Major glands
pituitary gland
thyroid gland
parathyroid glands
adrenal glands
pancreas
thymus
pineal gland
gonads (ovaries and testes)
(1) Pituitary gland
Pea-sized pituitary gland, located on inferior aspect of brain
called “master gland” it regulates many key processes
(2) Thyroid gland
Lies directly below larynx, partially in front of trachea
2 lateral lobes
one on either side of trachea
join with a narrow tissue bridge (isthmus), butterfly shape
(3) Parathyroid glands
4 parathyroid glands: posterior surface of thyroid
(4) Adrenal glands
2 adrenal glands: atop two kidneys
contains two distinct structures: adrenal cortex and medulla
(5) Pancreas
nestled in curve of duodenum, behind the stomach and extends to spleen
islets of Langerhans: alpha, beta, delta cells
Alpha cells  glucagon
Beta cells  insulin
Delta cells  somatostatin
(6) Thymus
located below sternum, contains lymphatic tissue
(7) Pineal gland
at back of third ventricle of brain
produces melatonin
(8) Gonads
ovaries (females) and testes (males)
2) Hormones
classified into three types: amines, polypeptides, steroids
(1) Amines
Amines are derived from tyrosine, essential amino acid found in most proteins.
(2) Polypeptides
protein compounds made of many amino acids connected by peptide bonds
(3) Steroids
adrenocortical hormones secreted by the adrenal cortex (aldosterone and cortisol)
sex hormones (estrogen, progesterone, testosterone) secreted by the gonads
3) Hormonal release and transport
Corticotropin (anterior pituitary) and cortisol (adrenal cortex): irregular release body rhythm cycles
peak in early morning
4) Hormonal action
Hormone reaches target site  bind to specific receptor on cell membrane or within cell
Polypeptides and some amines: bind to membrane receptor
5) Hormonal regulation
Feedback: information sent to endocrine glands-signals need for changes in hormone levels
* Feedback loop
- Simple feeback (simple loop): when level of one substance regulates secretion of hormones
ex) low serum calcium stimulates parathyroid gland to release PTH
PTH promotes resorption of calcium
high serum calcium inhibits PTH secretion
- Complex feedback (complex loop): hypothalamus receives negative feedback from target glands
Complex feedback: through axis between hypothalamus, pituitary gland, and target organ
Ex) corticotropin-releasing hormone from hypothalamus stimulates corticotropin by pituitary
 stimulates cortisol secretion by adrenal gland (target organ)
cortisol goes through bloodstream to effector cells: cause physiologic effects.
rise in cortisol levels inhibits corticotropin secretion by decreasing corticotropin-releasing hormone
3. Diagnostic testing
direct, indirect, provocative testing, radiographic studies
(1) direct testing: measures hormone in the blood or urine
special techniques minute hormone amounts
<Immunoradiometric assays>
* Immunoradiometric assays (IRMAs)
* Immunochemiluminometric assays (ICMAs)
<Radioimmunoassay>
* RIA technique: determine many hormone levels, incubates blood or urine
<24-hour urine testing>
measures hormones and their metabolites
<Nursing considerations>
Venipuncture
Explain that accurate testing may require several blood samples
taken at different times of day
physiologic factors (stress, diet, episodic secretions, and body rhythm)
(2) Indirect testing
measures substance a particular hormone controls but not the hormone itself
glucose measurements help evaluate insulin
calcium measurements help assess PTH activity
(3) Provocative testing
Stimulate underactive gland, suppress overactive gland
depending on suspected disorder
(4) Radiographic studies
CT scans, MRI studies
Routine X-rays: how an endocrine dysfunction affects body tissues
bone X-ray: for a suspected parathyroid disorder, show calcium imbalance