BIOL 380 Lecture Notes - Lecture 2: Chocolate Cake, Blood Sugar, Chemotherapy
26 May 2018
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BIOL 380 – Lecture 2 – 07/05/02018
What happens to nutrients in our body?
2 mechanisms prompt us to seek food
- Hunger is a physiologic drive for food that occurs when the body senses that we need to eat.
The drive is non-specific
- Appetite – a psychological desire to consume specific foods. It is aroused when environmental
cues – such as the sight of chocolate cake or the smell of coffee – stimulate our senses,
prompting pleasant emotions and often memories
- Anorexia: physiological need for food yet no appetite (infections, mood disorders, medications,
chemotherapy)
Why do we want to eat?
- Brain is the primary organ that produces hunger sensation
- Hypothalamus triggers feelings of hunger or satiation (fullness)
o Signals are integrated from nerve cells in other body regions and from chemical
messengers (hormones)
▪ Nerve cells: special cels lining the stomach and small intestine send signals to
the rai to idiate if they are full or epty (streth reeptors he there’s
food in stomach)
▪ Pancreatic hormones, insulin and glucagon, maintain blood glucose levels
• Whe you hae’t eate a eal your pareas starts to release
glucagon, tells your liver to release sugar
• Insulin is made when you have high glucose
- Hormones: chemical messengers secreted into the bloodstream by
endocrine glands to help regulate body functions to play an important role
o Feeling full (satiated) results from signals from the stomach and rise in
blood glucose
Environmental cues trigger appetite
- Foods stimulate our senses: sight, smell, taste, texture, hearing
- Social and cultural cues
- Learned experiences
What happens to the food we eat?
- Gastrointestinal (GI) tract (long muscular tube):
o After ingestion food goe through the process of
1. Digestion – the process by which food are broken down into their component
molecules, either mechanically or chemically
2. Absorption – the process of taking these products of digestion through the wall of
the intestine
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3. Elimination – the process by which the
undigested portions of food and waste
products are removed from the body
o A series of organs (such as stomach and
intestines) arranged ina long tube that work
together to process foods
o Sphincters: tight rings of muscles that control the
passage of food material from one organ to the
other (opening/closing passageway)
- GI tract begins at mouth and ends at anus
Digestion begins at the mouth
- Cephalic phase of digestion
o Hunger and appetite work together to prepare
the GI tract for digestion
o First thought of food (nervous system) stimulates
the release of digestive juices
- Chewing moistens the food and mechanically breaks it
into smaller pieces
- Saliva contains digestive juices secreted by the salivary gland in the mouth
o Salivary amylase begins starch digestion
(release glucose)
o Bicarbonates neutralize acids
o Mucus moistens the food and oral cavity
o Antibodies and lysozymes fight oral
bacteria
- Taste receptors detect distinct tastes
o Bitter, sweet, salty, sour and umami (food
particles need to be dissolved in a liquid
to bind to receptor)
- Olfactory receptors detect aromas of foods (required for specific types of taste)
- The mass of food chewed and moistened in the mouth is called bolus
- The epiglottis covers the opening to the trachea during swallowing
o Epiglottis acts like a tiny trapdoor covering the entrance to the trachea (windpipe). The
epiglottis is normally open, allowing us to breathe freely. The brain signals the epiglottis
to close during swallowing so food or liquid cannot enter the trachea.
- The esophagus propels food from the mouth to the
stomach
- Peristalsis is the muscular contractions that move food
through the GI tract
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The pH scale
- pH = potential of hydrogen
- measures the potential of a substance to release or take up hydrogen ions in solution OR
- pH is a measure of acidity or alkalinity of a compound
- pure water is neutral and human blood is close to neural
- tissues lining the stomach are generally protected from the effects of acidity
gastric juice
- gastrin – a hormone secreted by stomach lining cells that stimulates gastric juice
- gastric juice contains:
o hydrochloric acid (HCl) (secreted from parietal cells) denatures proteins, kills pathogens
and activates pepsin
o pepsin (secreted from chief cells) – ezyes hat digests proteis (it’s a protease – made
it its inactive form – pepsinogen, aka a zymogen).
o Gastric lipase (secreted from chief cells) – enzyme that digests fat
▪ **minimal – fat is not readily broken down in the stomach because fats are
hydrophobic – not easily accessed by enzymes
o Intrinsic factor (secreted from parietal cells) –
protein that helps in vitamin B12 absorption
Digestion in the stomach
- Chyme: a liquid product of mechanical and chemical
digestion in the stomach
- Mucus layer: protects the stomach lining from the acid
in gastric juices (protects against erosion)
- Chyme stays in the stomach for about 2 hours before it
is released periodically in spurts into the duodenum
Digestion in the small intestine
- Small intestine is composed of 3 sections
1. Duodenum
2. Jejenum
3. Ileum
- Ileocecal valve (sphincter) connects
the small intestine to the large
intestine
- pyloric sphincter connects stomach
to the duodenum
- Most digestion and absorption take
place in the small intestine
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