Lecture #3 Flashcards Preview

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Flashcards in Lecture #3 Deck (48):
1

Vision (sight)

perception of objects in the environment by means of light they emit or reflect

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Light =

visible electromagnetic radiation
Human vision: wavelengths 400 - 700 nm
UV radiation: < 400 nm; too much energy
Infrared radiation: > 700 nm; too little energy

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Anatomy of the Eye

1. Three layers (tunics) that form the wall of the eyeball
2. Optical components admit and focus light
3. Neural component:

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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

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Iris diameter controlled by contractile elements

Parasympathetic - narrows pupil
Sympathetic - widens pupil

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Pupillary constriction and dilation occurs:

1. When light intensity changes
2. When gaze shifts between distant and nearby objects

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Photopupillary reflex

pupillary constriction in response to light

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Emmetropia

normal eyesight fixed on an object >6m away

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hyperopia

farsighted -- cannot see nearby

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Myopia

(nearsighted) -- Cannot see distance

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Sensory Transduction

Retina converts light energy into action potentials

Rods,cones,and certain ganglion cells

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Photoreceptor cells

absorb light and generate a chemical or electrical signal

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Rod (photoreceptor) Cells

night vision or monochromatic vision
rhodopsin + cannot distinguish colour

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Cone (photoreceptor) Cells

day or colour (trichromatic) vision
Photospin + can absorb colour

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Outer Segment (photoreceptor cell)

Specialized to absorb light

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Dark

Light

In DARK, rods steadily release the glutamate = DARK CURRENT

Rods absorb LIGHT 􏰀 stops glutamate

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Principal Mechanisms of communication between cells

1. Gap Junctions
2. Neurotransmitter
3. Paracrine - secreted into tissures
4. Hormones - chemical messengers travel in bloodstream

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Endocrine system

glands, tissues, and cells that secrete hormones

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Endocrinology

organs that are traditional sources of hormones

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Hormones

chemical messengers that are transported by the bloodstream

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Target organs or cells

those organs or cells that have receptors for a hormone and can respond to it

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Peptide Hormones

-hydrophilic
- cannot penetrate target cell
- bind to surface receptors and activate IC processed

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Steroid Hormones

- Hydrophobic
- penetrates plasma membrane and bind to internal receptors
- influence gene expression
takes several hours or days

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Hormone Interactions

most are sensitive to >1 hormone = interactive effects

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Synergistic Effects

Multiple hormones act
together for greater effect

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Permissive effects

One hormone enhances the
target organ’s response to a second later hormone

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Antagonistic effects

One hormone opposes the
action of another

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Hypothalamus

forms floor and walls of third ventricle of brain
regulates primitive functions, but many are carried out by pituitary gland

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Hypothalamic Hormones

there are 8 hormones produced in the hypothalamus
6 inhibit the anterior pituitary

2 are released into capillaries in the posterior pituitary

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Posterior Pituitary Hormones

- nerve tissue not a true gland example oxytocin and ADH

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Negative Feedback

increase target organ hormone levels which inhibits the release hypothalamic and/ or pituitary hormones

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Growth Hormone

- many effects on the body
- liver produces insulin-like growth factors

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Hyper-secretion

Gigantism

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Hypo-secretion

Pituitary Dwarfism

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Thyroid Gland

largest endocrine gland
has 2 lobes
secretes T4, T3 in response to TSH
Secrete calcitonin

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Thyroid Disorders

Decreased TH at birth (congenital hypothyroidism)

Decreased Th at adult
(Myxedema)

Goiter - enlarged thyroid gland

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The Adrenal Medulla

- secretes norepinephrine and epinephrine
- increases alertness and prepares the body for physical activity

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Mineralocorticoids

regulates electrocyte balance
stimulates Na and K

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Glucocorticoids

Regulates metabolism, helps the body adapt to stressors
secretes in response to ACTH

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Sex Steroids

Androgens: male development

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Adrenal Disorders

Cushing syndrome - excess cortisol secretion, lots of fat

Adrenogenital syndrome (AGS)
enlargement of sexual organs, maculating effects on women

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The Pancreatic Islets

1-2 million islets - clusters of endocrine cells that secrete hormones that regulate glycemia (blood sugar)

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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

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Insulin

secreted by Beta cells
released after a meal when blood glucose is raising
stimulates cells to absorb nutrients, store and metabolize

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Diabetes Mellitus

Most prevalent metabolic disease in the world
• Disruption of metabolism due to hyposecretion or inaction

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Diabetes Pathogenesis

cells cannot absorb glucose
fat catabolism increases free fatty acids and ketones in the blood
chronic hyperglycemia

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Type 1 Diabetes Mellitus

5-10% of cases
insulin insufficiency
inherited

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Type 2 Diabetes Mellitus

90-95%
insulin resistance aka failure to respond to insulin

risk factors
heredity, age, obesity, ethnicity