66 terms

Endocrine System: structure and Function Part 1

The endocrine system
- Consists of a group of glands that produce hormones
- Works with nervous system to control and coordinate all other body systems
- Effects body systems by chemical stimuli
- Tissues other than endocrine glands also secrete hormones. Ie Brain, Digestive organs, kidney
- Travel through the blood to specific receptor sites.
- Exert their effects on target tissue
- the specificity of hormone-target cell interaction is determined by receptors in a "lock-and-key" type of mechanism.
- Regulation of hormone levels in the blood depend on a highly specialized mechanism called feedback
Hormone classification
- Steroid hormones: hydrocortisone
- Peptide/protein hormones: insulin
- Amine hormones: epinephrine
- Fatty acid derivatives: retinoids
Feedback mechanisms
- change in homeostatic environment
- signal sent to CNS
- Signal sent from CNS
- produce effect
- Body returns to homeostasis
Positive feedback
- Not common
- Increases the target organ action beyond normal.
Positive feedback
Classic example
- action of oxytocin on uterine muscles during birth
- Baby pushes on cervix sends signal to hypothalamus
- Hypothalamus manufactures oxytoxin
- Oxytocin is transported to posterior pituitary and released
- Oxytocin stimulates uterine contraction
- the loop stops when the baby leaves birth canal
Negative feedback
- Most common control mechanism
- like a thermostat
- lack of homeostasis of a hormone in the blood or body turns on the production of said hormone at the hypothalamus and pituitary.
- when homeostasis is returned, the loop is shut off.
Basic structure of a feedback loop
- An environmental stimulus occurs
- This stimulates the control center (aka brain-hypothalamus)
- Hypothalamic hormones stimulate the pituitary
- Pituitary hormones stimulate the target area
- The target area produces a change
- the change acts negatively or positively on the cycle.
- The "master gland" of the neuroendocrine system
- Constantly monitors the body's homeostasis
- analyzes input from the periphery and the CNS
- coordinates response through the autonomic, endocrine, and nervous systems
Hypothalamic hormones
- Release inhibiting hormones (turn pituitary off)
- Releasing hormones (turn pituitary on)
Release inhibiting hormones
- somatostatin
- Prolactin release inhibiting hormone
Releasing hormones
- Thyrotropin releasing hormone
- Growth Hormone Releasing hormone
Connection to pituitary
- Neuronal connection to the posterior pituitary
- Endocrine connection to the anterior pituitary
Hypothalamus and the anterior pituitary
- The hypothalamus secretes releasing factors to cause the anterior pituitary to release stimulating hormones
- These hormones act with specific endocrine glands to cause the release of hormones or stimulate cells directly
- This stimulation shuts down the production of releasing factors
- Leads to decreased stimulating factors and decreased hormone release.
The Hypothalamic-pituitary axis (HPA)
- Most feedback loops run through this axis.
- HPA mediates growth, metabolism, stress response and reproduction.
- is secondarily in charge of almost everything else.
Posterior Pituitary hormones
- manufactures in hypothalamus, but released from the posterior pituitary.
- Oxytocin
- Target is smooth muscles of the uterus and breast.
- Functions in labor and delivery, and milk ejection
- Target: kidneys
- Function: water reabsorption
Anterior Pituitary hormones
- Thyroid Stimulating hormones (TSH)
- Growth Hormone (GH)
- Adrenocortico-tropin Hormone (ACTH)
- Prolactin (PRL)
- Follicle stimulating Hormone (FSH)
- Luteinizing Hormone (LH)
Thyroid Stimulating hormones (TSH)
- Target: Thyroid gland
- Function: Thyroid hormone synthesis and release
Growth Hormone (GH)
- Target: many tissues
- Function: growth
Adrenocortico-tropin Hormone (ACTH)
- Target: Adrenal cortex
- Function: Cortisol release (androgens)
Prolactin (PRL)
- Target: Breast
- Function: Milk production
Follicle stimulating Hormone (FSH)
- Target: Gonads
- Function: Egg/Sperm production
Luteinizing Hormone (LH)
- Target: Gonads
- Function: Sex hormones
- Uncommon disease that occurs in adults exposed to continuously high levels of Growth Hormone
- Begins insidiously around 40-45
- A primary GH secreting pituitary adenoma is the most common cause.
- Leads to unwanted growth of bones and other soft tissue.
- occurs if high levels of growth hormone present before epiphyseal plates close
Clinical Manifestations
- Enlargement of hands and feet
- Distortion of facial features, lower jaw and forehead protrude
- Enlargement of soft tissue around eyes, nose, mouth and tongue.
- Skin becomes thick, leathery, oily
- may have peripheral neuropathy
Syndrome of Inappropriate ADH (SIADH)
- high levels of ADH without normal physiologic stimuli for release.
- Released despite normal or low plasma osmolarity
- Failure of negative feedback system
Syndrome of Inappropriate ADH (SIADH)
- Malignancy is the most common cause, especially small cell lung cancer.
- can also be cause by infections, head injury, COPD, and certain drugs
Syndrome of Inappropriate ADH (SIADH)
Clinical manifestations
- Water retention
- decreased plasma osmolality
- Increased glomerular filtration rate
- decreased urinary output
- increased body weight
- Vomiting Abdominal cramps, muscle twitching
- Cerebral edema
- dilutional hyponatremia
Syndrome of Inappropriate ADH (SIADH)
Collaborative Care
- Correct the problem
- Goal is to restore normal fluid volume and osmolality
- fluid restriction in Mild cases
- Drugs that block ADH action on collecting tubules in more severe cases
- Administration of hypertonic saline solution in cases of severe hyponatremia
Anterior pituitary hypofunction
Sheehan's syndrome
- infart/necrosis of pituitary following postpartum shock or hemorrhage
- Causes partial to complete loss of thyroid, adrenocortical, and gonadal function
- Marked ACTH and TSH deficiency
- symptoms appear hours to years post partum
Adrenal gland
- The gland located atop of the kidneys
- Cortex is the outer part
- Inner part is the medulla
Adrenal cortex
- secretes cortisol, androgens, and aldosterone (electrolytes)
Adrenal medulla
- Sympathetic nervous system control
- Secrete Epinephrine and Nor-epinephrine (fight or flight)
Adrenal cortex steroid hormones
- Glucocorticoids
- Mineralcorticoids
- androgens
- Regulate metabolism and increase blood glucose
- Critical to physiologic stress response
- Regulate sodium and potassium balance
- Contributes to growth and development in both genders.
- Contributes to sexual activity in adult women
Cushing syndrome
Etiology and pathophysiology
- Caused by excess of corticosteroids, particularly glucocorticoids.
- Most common cause is iatrogenic administration of exogenous corticosteroids.
- 85% of endogenous cases due to ACTH secreting pituitary tumor
- Other causes include Adrenal tumors and ectopic (abnormal) ACTH production in tumors outside the H-P-Adrenal axis (usually in the lungs or pancreas)
Cushing syndrome
Etiology and pathophysiology
Male vs female
- Cushing disease (ACTH secreting pituitary tumor) and adrenal tumors are more common in women aged 20 - 40
- Ectopic ACTH production is more common in men
Cushing syndrome
Clinical manifestations
Part 1
- related to excess corticosteroids
- weight gain most common feature
- hyperglycemia
- protein wasting
- Loss of collagen
- wound healing delayed
Cushing syndrome
Clinical manifestations
Part 2
- mood disturbances
- insomnia
- irrationality
- psychosis
- Purplish red striae on abdomen, breast or buttocks
Cushing syndrome
CM: Weight Gain
- Trunk (centripetal obesity)
- Face ("moon face")
- Cervical area (buffalo hump)
- Transient weight gain from sodium and water retention.
Cushing syndrome
CM: Hyperglycemia
- Glucose intolerance associated with cortisol induced insulin resistance.
- Increased gluconeogenesis by liver
Cushing syndrome
CM: Protein wasting
- Catabolic effects of cortisol
- leads to weakness, especially in extremities
- Protein loss in bones leads to osteoporosis, bone and back pain.
Cushing syndrome
CM: Mineralocorticoid excess
- may cause hypertension secondary to fluid retention
Cushing syndrome
CM: Adrenal Androgen excess
May cause
- pronounced acne
- Virilization in women
- Feminization in men
Cushing syndrome
CM: Adrenal carcinomas
- menstrual disorders and hirsutism in women
- Gynecomastia and impotence in men.
Cushing syndrome
Diagnostic studies
Part 1
- 24 hour urine for free cortisol.
- levels of cortisol above 80-120 mcg/day in adults indicate Cushing syndrome
- Low dose dexamethasone suppression test used for borderline results of 24-hour urine cortisol
- False positives can occur with depression and with certain drugs
Cushing syndrome
Diagnostic studies
Part 2
- Plasma cortisol levels may be elevated with loss of diurnal variation.
- CT and MRI of pituitary and adrenal glands
- Hypokalemia and alkalosis are seen in ectopic ACTH syndrome and adrenal carcinoma.
- plasma ACTH may be low, normal or elevated depending on problem
Cushing syndrome: DS
Associated findings that are not diagnostic of Cushing's
- Leukocytosis
- Lymphopenia
- Eosinopenia
- Hyperglycemia
- glycosuria
- hypercalciuria
- osteoporosis
Cushing Syndrome
Callaborative care
Part 1
- Primary goal is to normalize hormone secretion.
- Drug therapy indicated when surgery is contraindicated or as adjunct to surgery
- Goal of drug therapy is inhibition of adrenal function.
Cushing Syndrome
Callaborative care
Part 2
- Treatment depends on cause.
- Pituitary Adenoma treated with surgical removal of tumor and/or radiation.
- Adrenal tumors or hyperplasia is treated with adrenalectomy.
- Ectopic ACTH-secreting tumors is managed by treating primary neoplasm.
Cushing Syndrome
Callaborative care
If Cushing's develops during use of corticosteroids
- Gradually discontinue therapy
- Decrease dose
- Convert to an alternate-day regimen
- Gradual tapering avoids potentially life-threatening adrenal insufficiency
Cushing Syndrome
Nursing assessment
Patient medical history
- pituitary tumor
- adrenal, pancreatic or pulmonary neoplasms
- GI bleeding
- frequent infections
Cushing Syndrome
Nursing assessment
Part 1
- Use of corticosteroids
- Weight gain
- Anorexia
- Polyuria
- prolonged wound healing
- weakness, fatigue
Cushing Syndrome
Nursing assessment
Part 2
- Easy bruising
- Insomnia
- headache, back, joint, bone, and rib pain
- amenorrhea
- Impotence
- Mood distubances, anxiety, psychosis, poor concentration
Cushing Syndrome
Nursing assessment
Part 3
- Truncal obesity
- Buffalo hump
- Moon face
- Hirsutism of body and face
- Thinning of head hair
Cushing Syndrome
Nursing assessment
Part 4
- Thin, Friagle skin
- Acne
- Petechiae
- Purpura
- Hyperpigmentation
- Purplish Red striae on breasts, buttocks, and abdomen
Cushing Syndrome
Nursing assessment
Part 5
- Edema of lower extremities
- Hypertension
- Muscle wasting
- Thin extremities
- Awkward gait
Cushing Syndrome
Nursing Diagnoses
- Risk for infection
- Imbalanced nutrition
- Disturbed body image
- Impaired skin integrity
Cushing Syndrome
Nursing planning
Patient goals include
- Experience relief of symptoms
- have no serious complications
- Maintain positive self-image
- Actively participate in therapeutic plan
Cushing syndrome
Nursing Implementation
- Health promotion
- identify patients at risk for cushing syndrome
- Long-Term exogenous cortisol therapy is major risk factor
- teach patients about medication use and to monitor side effects.