chapter 25 man versus mountain. jon krakauer read about his climb up mount everest he reached the...

Chapter 25Man versus Mountain

Jon Krakauer

• Read about his climb up Mount Everest• He reached the highest and one of the coolest

places on Earth• Wind chill temperatures average -53C.• Some people survive the climb and some do

not. Why?

How is the human body organized?

• Like a car or a computer, the human body is made up of many parts working together in a coordinated fashion.

• The parts are organized hierarchically, so that smaller components are organized into increasingly larger units, which are themselves organized into more complex systems.


• Anatomy– is the study of the physical structures that make up an

organism.• Human bodies have an anatomical structure that

well adapted to living in certain environments and performing certain functions

• We evolved in the hot, flat savannahs of Africa– Environment favored big brains, bipedal posture, etc.– We don’t do well swimming at bottom of ocean or living

on mountaintops.


• For all living things, the smallest anatomical unit is the cell. Human bodies are made up of trillions of cells, each of which can be classified as one of a few hundred different types.

How is the human body organized?• Cells are organized into

tissues – layers of specialized cells working together to execute a particular function.

• Humans and other animals have four different kinds of specialized tissue – epithelial, connective, muscle, and nervous.


• An organ is a structure made up of different tissue types working together to carry out a common function.

• Stomach is composed of four different tissues for digestion.


• At the highest level of organization, organs interact chemically and physically as part of organ systems.


• Physiology is the study of the way a living organism’s physical parts function.

• Physiologists want to understand how organ systems cooperate to accomplish basic tasks, – such as obtaining energy from food– taking in nutrients to build new molecules during

growth and repair– and ridding the body of wastes.

Maintaining Homeostasis

• The body is an integrated system for processing inputs and outputs and maintaining homeostasis – the maintenance of a relatively stable internal environment.

Maintaining Homeostasis: Thermoregulation

• Like many animals, humans have an optimal temperature and are sensitive to temperature changes.– We can toleration external temperature changes over a wide

range.– We are extremely sensitive to changes in our internal

temperature. • Through thermoregulation – the maintenance of a

relatively stable internal body temperature – our body temperature is kept at a consistent 37°C (98.6°F).

• This is just one example of how the body tries to maintain homeostasis.


• How do we respond to cold temperature???– Conserving heat and generating more

• To conserve heat, the body performs peripheral vasoconstriction – the reduction in diameter of blood vessels just below the surface of the skin.

• This pushes blood from the skin to the body core, where the internal organs are, decreasing the amount of heat loss from your skin to the environment.


• To generate more heat, the body shivers.

• Shivering is the involuntary contraction of normally voluntary muscles.

• When muscles contract through shivering, they create heat.


• To help prevent overheating, peripheral vasodilation, or the expansion in diameter of blood vessels, increases blood flow to the skin, and evaporative cooling (otherwise known as sweating) cools the body by releasing heat to the air.

• We are doing a lot of sweating this summer?

Balance

• If vasoconstriction goes on for too long (helping to retain heat), frostbite may occur– Death of tissues caused by lack of blood flow

• During the Everest climb, they had more than the cold to deal with? What else?

Altitude

• At high altitudes, the percentage of oxygen molecules in the air is the same as sea level – 20% oxygen at sea level

• Problem is with barometric pressure of oxygen is much lower, as it is with all molecules at high altitudes. – Number of oxygen molecules banging around in a given

volume of the atmosphere – Lower pressure means few oxygen molecules bind to

hemoglobin in blood• Low oxygen in blood is termed hypoxia• Have serious effects on brain

How do you cope with low oxygen

• For condition of low oxygen, climbers train or acclimate their bodies to the low oxygen condition.

• Acclimatization– The process of physiologically adjusting to an

environmental change over a period of time. Generally reversible

• How long did they train? What did they have as a backup for the climb?

• Body increases output of red blood cells

Maintaining Homeostasis: Feedback Loops

• Thermoregulation does not require conscious thought.– Automated response (thermostat)– The body’s thermostat is the hypothalamus

• The hypothalamus is a structure that sits at the base of the brain, right above the brain stem.– The hypothalamus is responsible for a variety of

physiological functions. – It receives signals from many different sensors – specialized

cells that detect changes in the internal and external environment. • temperature, pressure, or solute concentration.


• The hypothalamus acts as a thermostat. It has a specific temperature set point below which a warning message is triggered that body temperature is dropping when cold outside. – When that happens, the hypothalamus essentially

tells the body to take corrective action.- What happens to blood vessels? What else happens?

– Signals are sent from the hypothalamus to their target tissues along nerve fibers.


• An effector is a cell or tissue that acts to exert a response on the basis of information relayed from a sensor.

• They act to cause a change in the internal environment.

• Once effectors have raised the body temperature, the sensors sense the changed conditions and the signals are turned off.


• A feedback loop is a pathway that involves input from a sensor, a response via an effector, and detection of the response by the sensor.


• In a negative feedback loop, the output of the circuit inhibits the input of the circuit, thereby helping to bring the system back to its set point.

• Opposite effect• Temperature goes up, bring temperature

back down to set point.


• In a positive feedback loop, the output of a system acts to further increase the input of the system.

• Delivery of child, blood clotting


• Hypothalamus regulates many body functions: hunger, thirst, and sleep. – Body’s main homeostasis control center– Key part of nervous system and endocrine system– Right below the hypothalamus is the pituitary

gland that releases hormones for homeostasis.

What happened on the climb down Everest?

• Hypothermia– A drop of body temperature below 35C (95F)

which causes enzyme malfunction and eventually, death

• Thermoregulation cannot do so indefinitely– Work takes energy. Need food for fuel

• The body uses the sugar glucose, a breakdown product of carbohydrate digestion, as fuel.

• When we eat carbohydrates, sugars are released and absorbed into circulation, and blood sugar increases.


• Some of this sugar may be used immediately as fuel for aerobic respiration in cells of the body.

• Whatever is not needed right away will be converted into glycogen – an energy-storing carbohydrate – which is stored in muscles and the liver.

• By converting excess glucose to glycogen, the body maintains a relatively stable blood-glucose level.


• Blood-glucose levels are controlled by endocrine tissue in the pancreas, an organ that functions in both the endocrine and digestive systems.


• In response to high blood sugar, the pancreas produces the hormone insulin, which binds to receptors on muscle and liver cells, signaling them to remove sugar from the blood.

• Insulin also signals these cells to make glycogen, using the sugars taken up from the blood.


• When blood-sugar levels are low, the body first prompts us to eat by sending a signal to the hypothalamus. If eating isn’t an option, the body begins to break down its stored glycogen.

• Glucagon, a hormone produced by the pancreas in response to low blood sugar, triggers muscle and liver cells to convert their stored glycogen to glucose.

Organ Systems

• The integumentary system serves to protect the body from damage. It includes the skin, hair, fat, and nails.

Organ Systems

• The muscular system is responsible for the movement of body parts. Skeletal limbs, the heart, and other internal organs all move with the aid of this system.

Organ Systems

• The skeletal system provides structural support for the body and includes the bones, cartilage, ligaments, and tendons.

Organ Systems

• The circulatory system pumps blood between the lungs and the body cells using the heart, blood, and blood vessels. These organs transport molecules all over the body.

Organ Systems• The endocrine system provides

communication within the body using hormones made by tissues including the hypothalamus, pituitary, thyroid, and adrenal glands.

Organ Systems

• The nervous system includes organs that sense and respond to information from all over the body. This system includes the brain, spinal cord, and peripheral nerves.

Organ Systems

• The lymphatic system transfers lymph fluid from tissues into the blood and includes the cells and organs of the immune system, such as the lymph nodes, spleen, and bone marrow.

Organ Systems

• The respiratory system is involved in the exchange of oxygen and carbon dioxide between the air and the blood. Respiratory system organs include the trachea, lungs, and diaphragm.

Organ Systems

• The digestive system breaks down and absorbs food molecules using organs such as salivary glands, stomach, small intestine, liver, and large intestine.

Organ Systems

• The urinary system is involved in the regulation of fluid balance in the body and the elimination of waste in urine. The kidneys and bladder are key organs in this system.

Organ Systems

• The reproductive system is involved in the development of offspring. Male organs include the testes and penis. Female organs include the ovaries and uterus.


• Osmolarity is the concentration of dissolved solutes in the blood.

• Among the solutes dissolved in the blood are electrolytes – ions such as sodium and potassium that are critical for nerve signaling and muscle contraction.


• Osmolarity is monitored by the hypothalamus as part of osmoregulation.

• When you are dehydrated – when you have less fluid in your blood – the concentration of dissolved solutes is higher.


• If the hypothalamus registers that the concentration of solutes in the blood is high, it will trigger a sense of thirst, as well as triggering the release of antidiuretic hormone (ADH) from the pituitary, which travels through the bloodstream and acts on the kidneys.

• The kidneys are the organ involved in osmoregulation, filtration of blood to remove wastes, and production of several important hormones.


• ADH signals the kidneys to excrete less water in the urine.

• By reducing the amount of water lost in urine, ADH causes more water to be reabsorbed by the kidneys back into the bloodstream.

• Water in the bloodstream dilutes dissolved solutes and lowers the osmolarity.


• Osmoregulation also depends on sensors that detect changes in blood volume and pressure, both of which depend on the amount of water in the blood.

How do other organisms thermoregulate?

• Because humans use internal metabolic heat to thermoregulate, humans are classified as endotherms.


• Animals that rely on environmental sources of heat, such as sunlight, to maintain body temperature are classified as ectotherms.


• Some organisms generate heat from nonshivering thermogenesis.

chapter 25 man versus mountain. jon krakauer read about his climb up mount everest he reached the...

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human body

body core

body of wastes

mountain slide

human bodies

internal temperature

optimal temperature

cold temperature