Lecture #3 Flashcards
Vision (sight)
perception of objects in the environment by means of light they emit or reflect
Light =
visible electromagnetic radiation
Human vision: wavelengths 400 - 700 nm
UV radiation: < 400 nm; too much energy
Infrared radiation: > 700 nm; too little energy
Anatomy of the Eye
- Three layers (tunics) that form the wall of the eyeball
- Optical components admit and focus light
- Neural component:
Fundus of the eye
Macula lutea -fovea centralis
• Pit in center
• Produces most finely detailed images
Optic disc
No photoreceptor cells
• If image falls on this area cannot be seen = blind spot
Iris diameter controlled by contractile elements
Parasympathetic - narrows pupil
Sympathetic - widens pupil
Pupillary constriction and dilation occurs:
- When light intensity changes
2. When gaze shifts between distant and nearby objects
Photopupillary reflex
pupillary constriction in response to light
Emmetropia
normal eyesight fixed on an object >6m away
hyperopia
farsighted – cannot see nearby
Myopia
(nearsighted) – Cannot see distance
Sensory Transduction
Retina converts light energy into action potentials
Rods,cones,and certain ganglion cells
Photoreceptor cells
absorb light and generate a chemical or electrical signal
Rod (photoreceptor) Cells
night vision or monochromatic vision
rhodopsin + cannot distinguish colour
Cone (photoreceptor) Cells
day or colour (trichromatic) vision
Photospin + can absorb colour
Outer Segment (photoreceptor cell)
Specialized to absorb light
Dark
Light
In DARK, rods steadily release the glutamate = DARK CURRENT
Rods absorb LIGHT stops glutamate
Principal Mechanisms of communication between cells
- Gap Junctions
- Neurotransmitter
- Paracrine - secreted into tissures
- Hormones - chemical messengers travel in bloodstream
Endocrine system
glands, tissues, and cells that secrete hormones
Endocrinology
organs that are traditional sources of hormones
Hormones
chemical messengers that are transported by the bloodstream
Target organs or cells
those organs or cells that have receptors for a hormone and can respond to it
Peptide Hormones
- hydrophilic
- cannot penetrate target cell
- bind to surface receptors and activate IC processed
Steroid Hormones
- Hydrophobic
- penetrates plasma membrane and bind to internal receptors
- influence gene expression
takes several hours or days
Hormone Interactions
most are sensitive to >1 hormone = interactive effects
Synergistic Effects
Multiple hormones act
together for greater effect
Permissive effects
One hormone enhances the
target organ’s response to a second later hormone
Antagonistic effects
One hormone opposes the
action of another
Hypothalamus
forms floor and walls of third ventricle of brain
regulates primitive functions, but many are carried out by pituitary gland
Hypothalamic Hormones
there are 8 hormones produced in the hypothalamus
6 inhibit the anterior pituitary
2 are released into capillaries in the posterior pituitary
Posterior Pituitary Hormones
- nerve tissue not a true gland example oxytocin and ADH
Negative Feedback
increase target organ hormone levels which inhibits the release hypothalamic and/ or pituitary hormones
Growth Hormone
- many effects on the body
- liver produces insulin-like growth factors
Hyper-secretion
Gigantism
Hypo-secretion
Pituitary Dwarfism
Thyroid Gland
largest endocrine gland
has 2 lobes
secretes T4, T3 in response to TSH
Secrete calcitonin
Thyroid Disorders
Decreased TH at birth (congenital hypothyroidism)
Decreased Th at adult
(Myxedema)
Goiter - enlarged thyroid gland
The Adrenal Medulla
- secretes norepinephrine and epinephrine
- increases alertness and prepares the body for physical activity
Mineralocorticoids
regulates electrocyte balance
stimulates Na and K
Glucocorticoids
Regulates metabolism, helps the body adapt to stressors
secretes in response to ACTH
Sex Steroids
Androgens: male development
Adrenal Disorders
Cushing syndrome - excess cortisol secretion, lots of fat
Adrenogenital syndrome (AGS) enlargement of sexual organs, maculating effects on women
The Pancreatic Islets
1-2 million islets - clusters of endocrine cells that secrete hormones that regulate glycemia (blood sugar)
Glucagon
secreted by alpha a cells
released between meals b/c of falling blood glucose
In liver: stimulates release of glucose
Adipose tissue: stimulates the release of fatty acids
Insulin
secreted by Beta cells
released after a meal when blood glucose is raising
stimulates cells to absorb nutrients, store and metabolize
Diabetes Mellitus
Most prevalent metabolic disease in the world
• Disruption of metabolism due to hyposecretion or inaction
Diabetes Pathogenesis
cells cannot absorb glucose
fat catabolism increases free fatty acids and ketones in the blood
chronic hyperglycemia
Type 1 Diabetes Mellitus
5-10% of cases
insulin insufficiency
inherited
Type 2 Diabetes Mellitus
90-95%
insulin resistance aka failure to respond to insulin
risk factors
heredity, age, obesity, ethnicity
